I believe what Fallout did is typically called retro-futurism. The term "post-modern" is already occupied and has a very different meaning.
I don't think Pattern Recognition really counts. Precisely when it was set was mostly irrelevant to the story and the "futurism" of the novel is largely due to the style of writing of William Gibson. It could have been set in the present or near future and nothing would really change.
Fallout, or its predecessor Wasteland, was probably inspired in part by works like Canticle for Liebowitz, which were just normal (dystopian) futurism at the time.
A lot of cyberpunk and space opera is like that, I think, particularly in art. Cyberpunk art is still enamored of '80s neon, fashion, the then-looming fear of Japan Inc., etc.
But Fallout is something different, because it embraced '50s retro-futurism from the beginning. (Though it got more obvious in the later games.)
> A lot of cyberpunk and space opera is like that, I think, particularly in art.
This is a really interesting observation, thank you.
If we use Neuromancer a rough start date for cyberpunk, there was nothing 'alternate' about the whole "future of neon and kanji" style. And Snow Crash made an effort to change with the times; the Japanese stylings get justified as a character thing instead of a cultural one and the psychedelic hacking gets replaced with a decent anticipation of Second Life. The Diamond Age sticks with the Japanese emphasis, but brings in China and India as major powers, and updates the sci-fi focus to nanotech.
But somewhere along the line the strength of the aesthetic sort of overwhelms the attempt at futurism. Gibson came back to the near future and present, Stephenson went to the past, present, and then the far future. The last really future-facing cyberpunk novel I can remember reading was Infoquake, and reviewers kept saying that was "practically cyberpunk" or "had elements of cyberpunk".
And then at the other end of things, Altered Carbon has humans as an interstellar species, but still gives us a half-white, half-Japanese protagonist getting pushed around San Francisco by rich people. Shadowrun goes all the way to magic spells and centaurs, but the videogames retain the rainy East Asian atmosphere. And Big Hero 6 proves it's an aesthetic you can export completely; it might be a PG superhero movie, but it's about a half-Japanese kid named Hiro having illegal robot fights in a neon-drenched "San Fransokyo".
I don't know enough to do the whole rundown, but I suspect you're right about space opera too: Star Trek and 2001 start off as a modern/futuristic vision, but endure as this weird near-googie style we recognize as its own entity.
I suppose some aesthetics are way more fun to look at than to actually live in - we keep them around for art's sake long after they fail to take root.
It seems to me that Stephenson just likes East Asia a lot, I wouldn't be surprised if it turns out he lived there. E.g. Cryptonomicon has detailed geography and economics of the region in play, many of the other novels have events set in there―and in the pretty recent “Reamde” he again spends plenty of story time in Xiamen and some in Manila, even though the book is set in the present and there's little cyberpunkish about it.
I'm actually sort of learning from these books about the vibe of the region, some scraps of relevant history, and the area's economic relations with the US. Because otherwise it's mostly fantasy land to me.
I agree that Fallout was retro-futurism; I'd forgotten there was a term for it.
As for Pattern Recognition, the postmodern label isn't mine. It's a massively overloaded term, certainly, and I know some writers cut off the "postmodern novel" era around 1990. But the sort of academics who include Paul Auster and David Eggers wrote about it as a postmodern work in postmodern theory journals. It's definitely not a clean example of "future in the past", since it could easily have been very-near-future - I suppose I mostly included it for the tone of an unanchored present, rather than the actual chronology.
I don't think Pattern Recognition really counts. Precisely when it was set was mostly irrelevant to the story and the "futurism" of the novel is largely due to the style of writing of William Gibson. It could have been set in the present or near future and nothing would really change.