I'm down to accomplish something along these lines. been working on it for some time.
1st approach was to share cookies and recent tags with phpbb.
2nd approach was to bring something like miniBB or punBB into a page within WP.
(works, but no cookie sharing, and everyone goest straight to the BB, and like html pages sites with message boards involved, no one reads, the just ask in the forum. Zzzz....)
3rd (current) approach:
To alter the function of WP so that recent posts, and comments move the entry into the newest position of the Cat and the Index.
so it behaves more like a BB, and less like a blog/archive.
(looks like it's over my head actually)
if any of that sounds interesting, let me know.