Maybe take a different approach to this and instead ask for separate crew chat in-game. That would do away with the need for Party Chat at all.
Being able to mute other crews and specific players means that this should be realistically doable as the discrete audio channels exist to some extent. Push to talk could be used to speak in global voice chat.
I'm on PC but I've long said I would prefer this as it gets around several issues... it would allow Xbox players the ability to talk in game while still partied up and keeping their comms secure. It would allow PC players to join Xbox players and not be afraid of the security risks with Party Chat on Windows.
That would be a more realistic request than asking them to change something which is not in Rare's control.