I've posted the initial spec document for the Forums Package (the new Bboard) at the now-usual location:
http://dotlrn.openforce.net/doc/forums.adp.
This pretty much summarizes the stuff we talked about in this thread, and formalizes things a tad more. I've started writing this code and will import it in the CVS tree shortly. I'm focusing on functionality and page flow for now, not so much individual page UI.
This document is not done, I will be updating it as things move along, and I look forward to more comments and suggestions!