There's a large problem wih proximity chat. The Tower area where players can go idle or visit are small, thus making proximity chat potentially really noisy. Sure, that may make the game area more, "realistic" in the social aspect, but I'd suspect most players don't want to listen to whiney little brats dropping f-bombs or rage screaming. However, with that said, they really need to create Fireteam chat for randomly grouped Fireteams, when queueing for a strike.