Tribes already have their own subforum on this forum. I've never minded the effort to use it. Things might be easier if there was something like the cafe, though I'm not a fan of the cafe and would rather just have the forum. Also, I've never really like the BBs in Maplestory. The line-breaks were weird and there wasn't a lot of space you could reply with. Given it wouldn't have to be exactly the same as Maplestory's BBs, I'd still rather just use the forum.

Support. My tribe members don't use the forums a lot, so this would be a good alternative.

Sounds just like cafe?
A cafe for tribes might see more use than forums since it's in-game, however I feel the people who care enough to use the tribe forum would provide better quality messages than those who don't bother.
If it worked similarly to cafe, server resets clearing the topics/board becomes an issue.

Moved to Suggestions!

Personally I think this would be a bit redundant with the tribe forums already in place here.