I think releasing flavored crunch would be a good idea, as well. I don't know that I'd want everything tied to a specific setting, but something generic would be great. Way back in 1E days, Kara-Tur wasn't part of the Realms. Heck, Kara-Tur didn't even have a map. It was purely a name for an abstract concept of vaguely Eastern D&D. I'd be more than happy to see that sort of release with either an appendix for the settings that have an equivalent sub-setting or web support for settings.
In some cases, it might make sense to have crunch included in a setting book -- muls and defilers/preservers in Dark Sun, for example. For the most part, I'd rather see things grouped by themes, though.