Yes? There's a ton of AI upscales coming out and they're becoming really good; plenty examples on youtube including iconic scenes from iconic movies. Perhaps another 12 months max before AI upscales go from enthusiast/amateur remaster community to commercial.

Having an AI generate 75% of the movie pixels that weren’t there in the original work doesn’t really count as a ‘remaster’ imo

It's what most of those "HD remasters" of film are doing. (Well, sometimes it's a human or a chemical/mechanical process rather than an "AI", but either way you're fabricating details out of noise and/or thin air).

I suspect that getting objective improvements from a 4K to 8K film scan would require extremely well-produced film and probably a large-format film like 70mm.

This will not magically make extra detail appear, though. Film does not have infinite resolution.