As far as weirdly specific fandom AUs go, one of my personal favourites has to be the one that goes “media A is actually a dramatisation of the events of a really high-concept tabletop roleplaying game being played by the cast of media B” - complete with trying to figure out who’s playing who.
AUs of this type can be arranged into several rough tiers, depending on how strongly the two properties differ in terms of medium, tone and genre.
On the low end, for example, you might have “Team Fortress 2 is a tabletop RPG being played by the cast of Overwatch” - same medium and genre, moderately different tone. (Though even this presents certain challenges; remember that Overwatch takes place circa 2070, so the setting of Team Fortress 2 is a century in the past - this is an historical RPG. Which might explain a thing or two!)
At the high end, the trick is finding pairs of properties where you can still come up with reasonable answers as to who’s playing who - it’s easy to fall into the trap of throwing wildly dissonant media together just for the weird factor. If your players are the cast of My Little Pony: Friendship is Magic, it’s going to be pretty tough to explain why they’re playing The Walking Dead while staying in character. (Though that doesn’t mean you can’t go dark with them at all; if that’s your preference, try having them play The Hunger Games instead.)
If you’ve never given it a try, I highly recommend it - if nothing else, it’s a fun exercise in character analysis.