It would only make it worthwhile if SE's ingame voice chat was equal or better then the main Voice Chat programs on the web.

Because if they are in anyway less... people will still require 3rd party programs. Just like they do in other mmos.

So SE would be faced with tons of work and more servers to handle that many people on voice chat at once time. And even with that people in larger guilds or multi-gameing guilds will still use 3rd party software.

I cannot see it being cost effective to SE to make ingame voice. I do not see that bringing in enough subs to warrant the cost of hardware and development time.