Go full science fiction and enable vertical or even upside-down roads for a 3D experience. :-)
Imagine an environment where ground/walls/ceilings always have gravity and one can build literal city mazes in horizontal and vertical directions. All that traffic going everywhere, oh my..
Really depends: In some areas it is quite advanced (rendering) and in others it is lacking / underdeveloped (editors / tooling). But there is an incredible amount of progress and also churn in keeping up with that.