Huh, I had a somewhat similar idea with: Shoble.com. Big emphasis on the ability to file your post under an arbitrary number of subforums via tagging, though. Threw it up a few months ago, but I couldn't figure out how to get a userbase and so I never added the features I intended to.

I definitely agree with you that anonymity's never going away, and _something_'s going to eat 4chan's lunch at some point in the future, in light of moot's complete lack of interest in improvement and features.