https://github.com/bloc97/Anime4K
Yes it "guesses" what the missing information is and populates it. Similar approaches will work for live action media too.
And successive video frames encode so much extra resolution that a single frame doesn't capture, so there's a lot of information to pull from.
I'll be happy to see higher res versions of digital stuff even if it means AI upscaling but as someone who loves messing around with photo and video gear for fun I will never not find film endlessly fascinating. Somehow the fact that that they had to do all effects practically meanwhile they had the technology to film it that was so detailed that it's still up to our current resolution standards is amazing to me.
I think it depends on the movie, 28 Days Later was shot on digital potatocams and looks awesome.
I'll have you know they like to be called canon XL1s ;)
But I'm not sure how much was actually shot on those. I know a fair wedge of the action was, as it meant that they could do multi-cam shots (low budget, more realism, etc etc), I thought that they used ARRL something or others for slower shots. But I could be misremembering.
Being a child of the 90s and of the digital era I am always endlessly amazed at the quality and potential of film. Every time I hear a story about how something more modern won’t even be released in 4K because they don’t have a high enough quality source because it's all digital I’m kind of saddened.