Interesting, this actually sounds pretty cool and potentially implementable. I like that you brought up gangs with a range of specialties instead of only gangs with a specialty because right away I thought to myself, "What about the masters of all trades, not the jacks of all trades?" What happens if most of a gang proves abundant in a subforum, but one or two others in the gang show the most activity in a completely different subforum? Do they just not get to be labeled as an expert to that because their gang overall doesn't have that image? Perhaps instead of tying this with gangs, we could create a whole new group feature which provides groups purely based on skills that would be displayed next to each member(i.e. a moderator would have his mod status, and under that picture text would write he/she is apart of the modding group, or the whatever group showing he is experienced in that field). Now that I think about it, maybe I'm just talking about forum bosses haha. Still though. I like Llama's idea.
I also agree with Llama that it'd be nice to see the private forums come back. Though, how about as soon as possible? It may not prove needed now to the already settled in members(and/or it may become the only active part of the forum, but I seriously don't think that'll happen), but let's have it ready to use so the new members have something to reach for, because the ability to join a gang and get benefits from it was really enticing when I first got on board here at TGTAP. It showed(theoretically at least)that you were being a productive part of the community, because no gang wants an ass to represent them.
Fully-integrated gang wars on the other hand, alone, is a big endeavor to apply, and it does require a good amount of people to participate which can be equally as tough. Also, the game we'd be using isn't something that just came out yesterday, and I don't need to say people naturally are more likely going to want to swarm to the newest thing(i.e. new consoles coming out every so years)than the predecessor. Then again, I've never played SA for PC, let alone the online version and don't know the traffic of it today so I'm not one to say anything there.