Fictional Fans

Oh no, the bodyswap fic sounds like a bad idea. I've actually found that with complete AUs, I have the opposite experience in terms of figuring out the worldbuilding - I have no way to tell which parts of the worldbuilding come from canon and which are original to the writer, and it actually confuses me more trying to separate them out. (In some cases I've read complete-AU fics as my first story and not even realized they were complete AUs, and that is also a terrible way to start, for the record.) And if I'm looking to read more fic in the fandom, it's usually because I am interested in aspects that are unique to the canon (not necessarily plot per se, but relationship dynamic stuff like loyalty kink or ideological conflicts or whatever), so I often find myself actively disinterested in fics that don't use it. And sometimes complete AUs will even completely change basic character dynamics - switching out which character is in a position of relative power, for example. In a canon-divergence AU, that's usually signposted as a major difference from canon, but no so much in complete AUs.

But if people were looking for only the characters, period, I can see how that would be less important.

I do think something like a coffeeshop AU or a Hogwarts AU is different from a more freewheeling thing like a fantasy AU, where authors often go wild - in the common formulaic AU settings, I can recognize the AU elements from the formula, so it's a lot easier to know what's canon and what isn't. At some point that fades into the suggestions up there about formulaic tropes and standard AUs. And of course that depends - I definitely wouldn't recommend the Imperial Radch coffeeshop AU for someone unfamiliar with the fandom!