I highly doubt it's going in. Its a MASSIVE pain in the ass to program, and considering it wasn't in the beta, I doubt it'll be in the full game.
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There is already a proximity system in place when taking to fire team members in game chat. You may have noticed that if a player was close to you they had a clear voice, but when farther away they sounded as if they were coming through a radio.
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That's not anywhere near the same as proximity chat for the entire game with players coming and going.