But why, if completely 3D GIS would be so super awesome, do you think that that decent tech stack doesn't exist? The answer is that for the vast majority of applications of GIS, 3D is just an unhelpful distraction.

I don't want to upset you, but I really think you are not speaking from a position of knowledge if you think otherwise (I have a couple of degrees in Geography including one in GIS specifically, plus 15+ years' experience in the field).