Not sure how difficult this would be, however I think it would be a nice feature to have non rated clan cooperation games against other clans. Every one in the clan gets to vote on the next possible move, and the clan leader chooses the winning move to make. It would be great to have it linked to the private clan forums so that there is an easy way for the clan to discuss the game and moves.
We are currently doing this on our clan, however the voting and discussion needs to be held at a different site for ease of use. It would be nice to have it all available here. I think it is a good way to get clans involved, and is also a good learning tool