Some suggestions for this mod (don't require big changes, but would improve performance and cohesion):
(1) add social group id & category to forumdata (bitfield) during social forum creation*
(2) honor the forum's thread icon settings within the social group thread display
(3) change navbits within social forums so that they match those of the regular discussions, allowing for easy navigation
*(1) would eliminate the need to query the database in the forumdisplay_start hook and would also let you do (3) without additional queries
If I find some extra time to implement these features, I'm willing to post them here. However, I can't exactly use my live board as a sandbox, and don't have a test environment handy at the moment, so hopefully you can get to them before I do