Short response: it's not as easy to answer that question as it once was. It seems clear that the primary state of the genre the past two decades is ubiquity. As the roots and branches of sf extend in all directions and intertwine with everything they encounter (and vice versa), as publishing becomes cheaper and easier, as publishers increasingly push more and more responsibilities onto the authors themselves, as social media has become self-proliferating, as ebooks have expanded the market, and as self-publishing has established itself, the market has become saturated. There are niches within niches within niches, and all are flooded. There are literally thousands of books and stories published per year—and that's just sf. To assume a single person can read even the majority and form an informed, overarching opinion is ludicrous. In short, the selection from which to choose pieces for our early 21st century sf museum is exponentially larger than it was a century ago. We are in a golden age—if quantity is the measure. But that is another story...
Making things even more complicated is that it's impossible to identify a center-point in the mass—a single locus around which science fiction trends are developing. Instead, there are multiple loci. The science fiction expert needs to specialize, and our museum requires a more complex setup to accommodate the current phase.
Perhaps the most obvious locus (if it can even be called as such) is genre combos, genre blends, genre milieu, trope mixes, device borrowing, cross-pollination, genre free-for-all—whatever you want to call the pile of spaghetti that is the current taxonomy of science fiction. Where in previous phases it was relatively easy to identify science fiction and its sub-genres (space opera, space adventure, time travel, alien encounter, BDO, hard sf, cyberpunk, etc., etc.), it's not as easy now. In fact, I assume younger readers don't give a fig for the definition of science fiction, so peppered across their reading experience are its devices. Like jazz, science fiction went through it's own evolution before expanding outward into all areas. Where trumpets and saxophones could be clearly identified with jazz of the early 20th century, one finds them in every form of music now, just as the traditional tools of sf are being mixed with all other forms of fiction today. The cross-pollination so great, in fact, I believe we're at the point where it's impossible to have a representative selection in the museum for every blend or mix. And here we have the 'steampunk-wild west-alien' representative, and on your right is the selection for 'time travel-telepathy-romance', and just behind you... It seems a futile exercise. (I wonder what the jazz museum does with its post-70s wing?) Regardless, it should at least be noted that contemporary science fiction (or “science fiction”) has penetrated and been penetrated by every other form of fiction.
Another of the largest, most visible loci is politicized fiction. Broader socio-cultural movements clearly an influence, character traits and life circumstances that were previously woven intrinsically into stories are now given the red carpet and appear more regularly. For example, non-cis, non-male, and/or non-white characters are more often identified with flags and whistles to draw readers' attention. (For a great comparison, see how David Gerrold's The Man Who Folded Himself was presented and marketed in the 70s compared to, for example, how Simon Jimenez's The Vanished Birds is presented and marketed today.) Similarly, settings or cultural environments that are outside the standard Western purvey (whatever that means) are likewise foregrounded with force. African, asian, native, and other ethnic elements—geographical, cultural, and otherwise, are pushed under the spotlight with pointers and tags in case readers should miss, for example, that the character is eating pho soup, not good ol' tomater', or just soup. (I personally prefer pho, but you get the point.)
Thus, similar to genre blends, politicized fiction is complexified by the number of branches extending from its locus. Multi-culturalism, liberalism, “feminism” *, traditionalism, lgbqt interests, pro-establishment, etc., all see dozens and dozens and dozens of stories published each year with relative themes or related elements. A museum section could be dedicated to each angle of these politics.
But when looking to position these pieces in the museum, an important external factor must be taken into consideration: politicization exists not only in the fiction itself, but likewise extends into the surrounding organizations and media. A great example of this is awards. Compare the authors, books, and subject matter highlighted today by such lists to lists just twenty years ago, and one sees a contrast. I understand there is an argument to be made that every era's politics have been recognized in fiction to some degree, which I would agree with. But what we're seeing today is a degree of pro-activity like never before. Rather than media, authors, readers, etc. reacting to the fiction being produced, there is an active promotion of the fiction which aligns with said channels' political views, and demotion, albeit most often indirect, when it doesn't. (I am, of course, ignoring comments sections.) It feels at times that books are pre-ordained to succeed in certain environments. If an author includes the socio-political elements aligned with media channel Z, Z will often laud the work, regardless of its actual quality.
Therefore, a note needs to be added to the plaque on the museum wall beside politicized fiction: “There was a push for representation over quality”. To be clear, this is not to say all heavily politicized fiction is poorly written. No. This is only to say that the importance of excellence in story-telling has given significant ground to political interests as the broader cultural landscape transforms the past couple of decades. More and more often books/stories are selected for recognition based on their extrinsic rather than intrinsic qualities. Let's elaborate.
If your political interests lean toward everyone-gets-a-trophy, then representation over quality may not be a bad thing. Diversity and inclusion are indeed laudable. Trouble is, not everyone does get a trophy. In fiction this also opens the door for lower standards, not to mention sends the message: “Unless you write fiction with politics that align with Z's interests, you won't be recognized or promoted by them--by the right or left”. Given the heavy state of competition on the market, political angles quickly become marketing pitches, and thus artificial motivation (for some). I would guess there are a number of writers today, for example, who say to themselves when starting a story: “I think I'll include a female hero, regardless whether it naturally fits the story I have in mind, because I know there is a greater chance the story will be recognized for it. And I'll give her a sword, because the gods know there are not enough book covers today featuring people with swords.” Now, if the market demanded overt female heroes, I could understand. But the overt ones—the heavily politicized version—don't tend do well on bestseller lists. But I get ahead of myself. More to come.
Overall, today's socio-cultural environment doesn't seem equipped to produce the best fiction humanity has to offer. Historically, competition of ideologies and openness to differing opinions has seemed to produce stronger offspring. (To be 100% clear, this applies to both the left and right as they distinguish themselves today.)
Working from this, the value shift toward politicized fiction over quality or innovative fiction means a lot of the stories which receive recognition are merely mediocre. They're not poor, they're not trash, they're not pulpy. I call it the Clarion curse: books that have been peer-reviewed, either literally or figuratively, to the point of becoming acceptably vanilla. Please everybody and you please nobody—except those with similar political interests. On awards lists today less often does the reader regularly find books with numerous flashy turns of phrase, experimental approaches to structure or viewpoint, or signs that the envelope of what fiction can be in the 21st century being pushed. Most simply replace white/western/traditional elements with non-white/non-western/non-traditional elements, or, vice versa, a doubling down on those elements in order to fight back against the left. (If you want to torture yourself, see the horrendous novella Sunset Mantle by Alter Reiss as an example of the latter.)
From certain perspectives, representation can be considered “healthy”. I understand it is empowering for the groups represented, and does add diversity and variety to reader choice (more in a moment, I promise). But to foreground work which does not possess complementary quality in the other, universal aspects of writing simply because of its politics or demographics is a bad road to be on. Thus, my concern is that a solid portion of the fiction representing the modern era in the museum of science fiction will be of Clarion quality. But I know, I know: the museum doesn't care about my personal opinion. It cares only about what is.
To be fair, a huge chunk of fiction in the museum from the 1920s and 30s is complete trash—like high schoolers' homework. Thus, it's important to comment that mediocre today is still better than noteworthy then. It's equally important to recognize that the shift to politicized stories has brought a breath of fresh air to science fiction in many ways. Check out the blurbs and cover art for space opera (which is still being produced in large volumes today despite the lack of major publicity) and it looks relatively boring. Do I read the same-old, same-old space ships blasting away as men vie for ageless power, or take a chance on this new book about a Nigerian girl who discovers voodoo powers granted by aliens whose interests in humanity are ambiguous? The degree to which the author of the book about the Nigerian girl leans on the novel's political commentary, as well as their own demographic, seems to play a strong role in its potential for recognition, just as the degree to which said author tries to tell a more universally human story with properly balanced, interwoven ideas and technique seems to play a role in its potential success on the market. Which leads us to the third section of the museum...
What is happening in the world of science fiction awards and media is contrasted by bestseller lists. The so-called 'classic' stories without overt politics—revenge, conflict, drama, murder, love, war, mystery, etc., all these continue to sell well. It's rare to see a politicized novel recognized by awards sustain success on bestseller lists. Stephen King, a talented writer who doesn't give a flip about left or right, continues to sell immensely well. James Corey sells copy after copy by writing space opera with only mild political undertones. The Chinese writer Liu Cixin has hit US bestseller lists on the strength of idea sans politique. Dune, for goodness' sake, continues to be quite popular. Certainly a few, heavily politicized books pop on and off the bestseller radar, but few stick around long. My assumption is that the readers of popular/mainstream science fiction either are oblivious to what is happening on the politicized side of things, or choose to ignore it in favor of authors/stories they like or are interested in regardless of politics. For that, they are a force that must be represented. Thus, into the museum we will likely be putting a number of books and stories that did not see the light of awards but which did see the light of millions of people's bedside lamps.
And there is a fourth group representative of our times, one you don't immediately think of but which is a major force: fiction in board games, graphic novels, comics, and rpgs. In case you were unaware, such narratives have become a force in the world. Dozens upon dozens upon dozens of major publisher and Kickstarter projects occupy this sphere, many of which are sf. Where rpgs were once the domain of Dungeons & Dragons, for example, there is a growing number of such games on the market, some of which also dip into sf. Granted, interaction of some variety sits on top of these narratives, but to dismiss these stories as 'just games' would be a disservice. Arkham Horror: The Card Game features tales that have a surface layer of horror, but a deeper layer with strong aspects of fiction, everything from pulp adventure to existential inquiry. Waste Knights 2ed comes with a book, an actual bound book, full of story threads featuring moral ambiguity. Cyberpunk 2027 is a major force in the rpg world, it too with its own questions what it means to be human. And that is only tabletop games. Comics and graphic novels have likewise EXPLODED. Given this, the museum would not be complete without their recognition.
And there is still a fifth and final portion of sf in need of representation in the museum: the unknown. A lot of, if not all of what goes into museums is in hindsight. Where galleries are home to both the newest and oldest, museums only look backwards in time. Thus, likely there are currents and undercurrents of science fiction that are not clear at the moment but in a few years will be brought to full light, and thus in need of wall space in the science fiction wing.
In summary, our sf museum of the early 21st century is likely to contain: science fiction blends and mixes (somehow), overtly politicized fiction, broader appeal/marketable sf, sf from analog games, and the unknown (fiction which may reveal itself in hindsight). If you've read this far, you're probably disappointed. You wanted me to name individual stories; who exactly will get into the museum—the draft table of contents for Shippey's next volume. I wanted to, but I don't consider myself well-read enough. My interests are more like the gallery: spread over time rather than focused only on the here and now. I'm a dilettante, I know.
What's next? What should the museum plan on putting in the space designated for mid-21st century sf? For example, will said space be unnecessary as the notion of “science fiction” is swallowed and spread across the broader expanse of fiction? Will the divide between the left and right expand further in story form? Or, will it collapse back to a more moderate state? Will additional factors emerge to disrupt sf? Can heavily politicized fiction gain traction on bestseller lists? Will the flood of fiction disperse as other, narrative-driven mediums like film, tv series, video games, board games, or rpgs gain prominence? Will WW3 destroy everything?!?!? Only sf knows the answer.
*Feminism is in quotes because I'm not sure what the term means anymore. Where feminist movements of the 19th and 20th centuries had agendas and rallying points, feminism today has no such center—at least that I can observe. Media seeming to have utterly fragmented what feminism might collectively mean in the early 21st century, I have to put the term in quotes. I thought about using the term 'female empowerment' given the large number of narratives that revolve around the idea, but ultimately felt it was insulting. So, quotation marks there are.