I don't think the voice chat issue is ever going to be solved on consoles. I can't imagine a world where a game disables party chat for teamwork purposes. Not even sure if Microsoft would certify a game that did such a thing.
My proposal for a compromise to discourage using XBL party chat:
When you group up with people via the in-game party system, you are automatically added to an open-mic voice channel with them. When the game starts, you'll also receive audio (maybe at a slightly lower volume) from non-partied players. You can communicate in the regular game chat channel via a d-pad press.
Iirc Gears of War used to make switch to game chat to play ranked games.