As far I can see it is possible and good enough today with Skype, FaceTime and so on plus a good internet connection; yet people prefer email, chat, telephone ... I think that is what is holding it back and because of the lack of demand there is not really big investment in create hardware and software to support it.
I am pretty sure that I can do a high quality FaceTime call with a number of people.
Yet still I prefer doing a regular phone call. As so does just about everyone else. The question you should ask is: Why is that?
It is not a technical problem.
A number of people that could afford $1000+ to be able to use that platform.
I personally wouldn't consider this problem to be technically-solved until an Android that can barely be considered as a mid-ranger can do it.
For the most part, given the margins at the high end, it's not significantly better.