Thank you for taking the time to explain! I can certainly understand why you (and so many others) find the various kinds of AUs fun, intriguing, almost like an intellectual exercise. The setting-change AUs that require assigning characters to Hogwarts houses, dæmons, bending types, and so on are almost like an extension of the various quizzes and communities where people can Sort themselves, find out what their dæmon would be, etc, and given that fandom is all about thinking intensely about characters, putting them in those kinds of AUs makes sense.

Time travel (whether in fic or original fiction) has to be extremely good for it to work for me, so I agree with you there.

That crossover between Rogue One and the Goblin Emperor could definitely work!