AIUI, the forum idea was tried for Overcomingbias.com back when it was a shared-authorship blog. It didn't quite work out.
There's plenty of opportunity to hash out lower-interest points here. In addition to the monthly open threads, just clicking on "Recent posts" in the sidebar will bring up a list of posts which didn't make the front page.
1matt
Some life hacking: narrow the distance between "I wish" and "I will". Shared hosting starts in the realm of $5/month. Open source forum software is very available. With fairly basic computer skills and Google you're probably not more than 6hrs away from having the forum you want. Some early research might narrow that gap further.
Hear ye, hear ye: commence the discussion of things which have not been discussed.
As usual, if a discussion gets particularly good, spin it off into a posting.
(For this Open Thread, I'm going to try something new: priming the pump with a few things I'd like to see discussed.)