Guest posts/Public Q&A : we could invite "celebrities" (other bloggers, mostly) to either write a guest post about a topic they care about, or just answer questions from the community. For example a feminist blogger, or Razib Khan, or, I dunno, someone that has interesting things to say but isn't part of this community.

This would be different from a "normal" post in that we wouldn't expect the poster to stick around much, wouldn't chastise him for not "fitting in" ("Have you read the sequences?") or for linking prominently to his own blog, etc.