I think making restrictions for all players because someone is abusing current rules is like making knives forbidden for all people, because someone has used knife to kill somebody. Much better idea is making real punishments for such things, for example ban for whole season, just for guilty player.
If You think there is some kind of unfair competition, just report the player and give some kind of proofs. Just playing with teammates is not anything bad. Show the replays which are proofing that those games was fake and let people vote if there were something illegal. Actually I checked just few whitelords games and see just one which maybe was a fake:
http://www.warbarons.com/ver101/replay/ ... _whitelord I guess admins can check IP/MAC adresses of players so can eliminate and punish for multi accounts problem.
I suggest to add option: "ask for draw" so players can cancel the game if they don't like to finish it (instead of surrender). Because here, maybe just Gil realized that he has more important things in real life than playing another big map in Warbarons? For me 1 game is not enough to punish anyone. If You wish look for more and give us the replays. We will judge then.