I'm positive voice chat will never be included as a native option in pvp.
Its a sure way of letting people win-trade (already happens very commonly in wolfsden) and informing friends on other GCs, what their current GC is doing.
AKA cheating like hell.

There are a myriad of free voice chat software out there already, and if people really want to chat/cheat, they have many options.

But yea map marks could indeed be useful.