This would be a great feature for for those team games with total strangers. Hurdle: The only problem I see is that someone could switch teams after listening in on strategy. What kind of advantage could they gain by doing that? I don't know. A small price to pay for something I think would be very useful.
Due to the changing on the fly lobby... probably not the best addition. Just do your pre-game chat before you select a spawn. Either that, or play with people you know. I never play team games with randoms.