I was thinking of the same thing. What is really needed is a clean group management solution with a nice inviting UI, a good spam filter (something like Akismet) and good access control for various levels of admins. The last would really hit it off with open source projects having a BDFL sorta guy with multiple pillars.

It could even be freemium with free access to public groups involved in open source projects. Maybe even some nice integration with whatever seems logical.