The two movies that suggest the beginning of true genre identity are Children of Men (2006) and Never Let Me Go (2010), both based on recent books. These represent the plateau of certain trends in science fiction that have been building for a while, and they firmly plant themselves within some boundaries that have been established by a bunch of other movies, as discussed below. And I think there are going to be more like this. I can sense it just over the horizon.
The main thing that strikes me about Children of Men and Never Let Me Go is that both are understated films built upon science fiction premises, whose thematic sights strongly diverge from that premise, and instead converge upon broad social themes. Children of Men is about society's fascistic responses to crisis, and Never Let Me Go is about the sacrifices made by individuals in service to the vast, impersonal social order. Of course, there are stylistic similarities between them, as well... understated, gritty palettes, the use of the photographer's eye to capture the beauty of the mundane. But the genre identification is more about the set-up and follow-through.
Of course, science fiction has long wrestled with social problems. Zombies, evil artificial intelligences, man-made monsters -- it's all about our enthusiasm and anxiety over progress and social control, right? But going back, very few films engage with broad social conditions like these new sci-fi films are doing, or locate these conditions in individual experience in such a direct, unsensational way.
Still, it's not entirely without precedent. Strange Days (1995) is a direct precursor to this cinematic movement, and echoes can be felt as far back as Godard's Alphaville (1965). Terry Gilliam may be considered a direct forerunner, as well, with films like Brazil (1985) and 12 Monkeys (1995). These don't have the strict realist impulses of the Cuaron and Romanek films, but they do have the interest in creating complex social relationships within a speculative setting. On the other hand, there is at least one recent sci-fi film with a deadly realist impulse, but without the social engagement shared by the films listed above: John Hillcoat's 2005 adaptation of Cormac McCarthy's The Road, which is gritty and deadpan (i.e. "realist"), but which handles its sci-fi premise with an intensely traditional hero-myth structure. You might attach Blade Runner and Alien to that side of the genre boundary, as well.
It's a central tenet of these speculative realist films that they eschew two frameworks that are usually central to science fiction... first, the mythic hero structure centering on a messianic central protagonist; second, the utopian framework that drives most science fiction to either applaud or condemn human progress. Obviously Never Let Me Go has almost no trace of a hero's journey... if anything, it has the gray struggle of gothic romance, eventually leading to acceptance and resignation in the face of an unsympathetic world. It's also mercilessly uninterested in portraying any sort of utopia or dystopia. It portrays progress from the perspective of progress's victims, and it does not sit in judgment of this system, sanctioned by the society, which is so cruel to a chosen few.
Children of Men is a little more heroic, and a little more openly dystopian, but it still downplays both of these frameworks. It's only about a dystopia in so far as it shows a society that's broken down in an attempt to preserve itself... unlike 1984, there's no sense of sinister dominance or absolute control. Rather, the whole film shows entropy and decay winning out over the cynicism of a fascistic government. And as a hero, Theo doesn't win any mythic warrior awards. He protects his charge, as he's been hired and obligated to do, and he's admirable in his loyalty, but his role as a protector is purely secondary to Kee's role as savior of the human race. The film's quiet, unsentimental ending shows us just how insignificant Theo was... how he was essentially an observer, a dedicated servant, and that the true work of saving the species is a much longer journey, of which we have seen only a fragment.
This both connects and distinguishes these films from some recent close relatives. In particular, I'm thinking of District 9 (2009), which certainly starts out as a speculative realist film, a science-fiction film transplanted into a very modern morally-ambiguous social ecosystem. As promising as it was, District 9 eventually mutated into a heroic rebel fantasy, with the transformed Wikus as the token boundary-crossing hero figure, and the apartheid South African society as an oppressive dystopia. Stylistically, the pseudo-documentary format of the film was also too self-conscious to quality as realist. In all traditional realist filmmaking, the eye of the camera is purely transparent, built to preserve continuity and present the characters in a direct, lucid style.
Gareth Edwards' debut feature Monsters (2010) has a similar profile to District 9... it's built around an interesting speculative social reality, but eventually becomes about the main character's acceptance of the hero/savior role, his personal journey of enlightenment, and the traditional romantic love story that ensues.
How about Duncan Jones' Moon (2009)? Another contender, but in that case, I think the setting was too remote from the everyday social reality that it was working to establish. By taking place in an isolated space station, and by adopting certain surrealist tropes, Moon became a direct psychological investigation, more of a cerebral rubik's cube, rather than a film of human experience shot through with social reality.
What connects and differentiates Children of Men and Never Let Me Go is hard to pin down... the sense that they're taking place in an unpredictable, unplanned outside world, controlled by ambient social and political forces... that much of the action is improvisatory and reactive, and that "fate" and "destiny" are conspicuously absent... that ideals and ethics are a loose, unreliable veneer over a wilderness of id and instinct... all these implications are present, and important to the soul of the genre.
There IS one other film that I think belongs squarely in this genre space, and it significantly precedes the two recent ones I've mentioned. This is Michael Haneke's Le temps du loup / The Time of the Wolf (2003), and though the premise isn't exactly high-concept (society breaks down for some reason and everyone becomes a refugee), it does pursue that premise with a relentless eye for the social realities of a struggling populace. It watches like a case-study of what would happen if you took a rural society, with its expectations for comfort, security, and civility, and hit the reset button on its hierarchies, power structures, and property ownership. It doesn't hurt that it's beautifully poetic and humanistic at its critical moments. It is a film that will stick with you.
There are a few that might qualify that I haven't seen yet. Spike Jonze's Scenes from the Suburbs might be a great reference point for this emergent genre. I won't know until I get to check it out, though.
I think it would be lovely to see Jim Jarmusch take on a serious science fiction project... this would be a great area for him to contribute some work. And I can think of one or two novels that would be pretty sweet if you adapted them as speculative realist films: how about Ursula LeGuinn's The Dispossessed, for instance?