Now imagine if anyone could casually just fork a piece of writing and adapt to their personal tastes. "Like this, but make X be in love with Y instead of Z. Also make Z not really die but make a surprise comeback in the final chapter." It might be fun to play with such capability for a moment or two, but I can't imagine anyone enjoying exchanging such stories - if everyone can trivially change anything, then everything becomes arbitrary. There is no story, only everyone looking at their own selfie.
Incidentally, GPT-3.5 and GPT-4 already give us this capability with smaller pieces of fiction. You can literally alter any short story like I described above, today. Anyone can. And somehow, I don't see any takers. I think people realize there's no entertainment value in it. Hence, this is what might just save Hollywood et al.
Erotica is one exception to what I described above, as it's by nature the kind of fiction to be enjoyed personally, not in a wider context. And, of course, erotic story generators are as old as the Internet.
Writing, even prompting, is more work than reading, and it takes some of the fun out of it - plot twists are no fun if you told someone what they should be.
Plain ChatGPT still requires a bit back and force to get complex tasks going, but Auto-GPT already has a loop around it that makes it possible for GPT to feed into itself and perform complex tasks that are beyond a singular prompt line.
Even without that, ChatGPT can already provide quite serviceable short stories, with no effort on the user beyond "write a short story". The biggest practical show stopper right now is that ChatGPT has strict filtering, so the moment you have guns, action and death, the story just ends. BingChat is even more extreme with the filtering and will fail almost every time.
So no John Wick fanfic then