It would be a gameplay mod, so no weapons would be changed. You would start out as a free-for-all. But once you killed someone, they would spawn back on your team!! And if someone else shot them after then he would change their team! This would then continue tell there is only 1 team left!! I would find this really enjoyable! Kinda like Dodgeball.
That actually seems like a very innovative idea, if someone can make that, id be sure to download it. Great idea, although it would get very one sided at the end. :P - doh!
Only problem is it would probably take to much to do. Since you gotta have one person start out as allies and one start out as Axis and then be an ffa. but as the game is now you have to be either axis or allies.. Possible. WOuld actaully be cool to see..