I think the addition of voice chat could be great but just in certain parts of the game, like partys or group raids. But it comes with a big problem: Moderation. If you want to report someone because he said something in voice chat, there is no way to prove it, unless you got a system that records every interaction in the voicechat which is very difficult.
We are going to feature voice chat in the game, and most probably it will be integrated if not in the next test, the one after that :)
That way we will have more time to test and tweak it, and to be ready an fully functional when we go for Release.