That dream quickly died when it became apparent that 98% of the people can't even handle 2 dimensional driving with much competence (many even have trouble with just one - see any left lane around the country), so adding another dimension would result in one big blood bath
My point was that the future isn't what it used to be. All of the wonder and big thoughts seem to be squeezed out of it. Some time in the future why can't a sufficiently integrated computer system take human input commands and flight plans to create a safe three dimensional air space?