Remathilis
Legend
Hey now, some of us grew up in "The Known World" and there's a lot of classic adventures set there. I'm not expecting a world book, but like you said, they've borrowed other items, no telling what will peek out next.
(And there's a fairly active online presence for it, but I think they mostly play BECMI retro clones.)
Oh, I understand, I'm one of them. I harbor no delusion though that if you ask even fairly avid gamers to name D&D worlds, Mystara wouldn't rank in the top ones named. Mystara/known world fans tend to either play BECMI (and borrow some from the 2e/Red Steel stuff) or are willing to convert stuff on their own and are perfectly content that their setting remains overall ignored (and thus saved form retconning and updates) save for the occasional bit of crunch cribbed when its officially converted later.
Mystara: flying under the radar since 1990.