Wiki – Work with developer of bp-wiki (doesn’t have to rely on BP) to replace MediaWiki.
Search – Without a clue how difficult it’d be, I’m just gonna go ahead and say: BuddyPress.org’s collective site search is one of it’s coolest features by far.
Support Forum – Time for a couple paragraphs.
I’d suggest taking a lesson from the biggest forum “2.0” (I hate it too) services on the web today, the likes of GetSatisfaction and StackOverflow. I think these are both brilliant services, based on very simple principles. Taking what I’ve learned from these sites and past forums, I’d suggest the following:
1) Don’t do bad vs good votes, just to good vs better. When someone gives an answer, it’s either worthless (don’t read that as negative), helpful or perfect. Very rarely is a topic downright the opposite of helpful, in which case it should be reported to a moderator, not just taunted with red votes.
The best replies should logically receive a lot of positive votes and be placed up top, while moderately helpful replies should follow suit. Then if you scroll further down you’ll just be looking at a bunch of ‘reaction’ comments or maybe some of the comments that helped find the way to the answer, but by themselves explain nothing.
2) Good system for ‘related threads’. There are some great WordPress plug-ins providing the base functionality for it already. When I ask “how to make a post?” and all I find, maybe because of a bad search, is “how to make a page?”, then when I check that page I’ll find the one I was actually looking for among the relateds.
3) There should definitely be a way to merge threads. Moderators should have open access to it, users should be able to recommend it (see #4)
4) “I also have this issue”-votes (also acting as opt-in subscription to thread) are great for avoiding duplicate threads and unnecessary “+1” and “me too” replies.