since the 3rd dimension (height) would likely only come into play on ascension and descent. I suspect if it ever takes off (pun slightly intended), that traffic will be confined to an altitude at which point traffic is back to two dimensions...just at a different altitude. Ascension and descent could be no more difficult than navigating a steep ascent/descent down a mountain road.

When it becomes mainstream, I would imagine that roads might be digitally maintained and people will have to constrain themselves to those roads or face some penalty (maybe we can vaporize them out of the sky). I would like to be around to see how we address traffic in the skies.