One of the biggest things holding back flying cars is the human element. We're not that great. And air traffic control for humans would suck. Transition to a future without human drivers. Then that problem goes away and we can have flying cars. We're already doing extensive work in automated drone piloting. Is it really that hard to imagine flying cars as a next step?
Self-driving cars, have a lot of perks in terms of infrastructure. They reduce traffic, so road expansion to mitigate traffic is reduced. They can park on their own, so there doesn't have to be parking everywhere, since your car can drop you off then go find parking. Flying cars increase those perks. At the point where we have flying cars roads are only need for long haul transportation, and so we can spend a lot less money on them. And if you reasonably assume vtol, parking lots can be extra dense.
And if we want to cast our gaze further forward. Once we have ubiquitous flying cars why would ground level even still be an important thing. we can all have aerial egress. no more going to a central shaft to go up and down. At that point cities might end up looking more and more like the worlds of the Jetsons, or the 5th element.
Perhaps we'll even moving to ocean based habitats, either floating or in platforms high above the sea, leaving the land to be a nature preserve with only small groups of luddites left. But, of course this magical future has the pitfall that as technology becomes like magic, a crash in society takes us back to square one. In which case our ocean based super-society will be just a legend to the luddite remnants of civilization left on the mainland. But that particular scenario was deliberately picked to sound like the legend of Atlantis.
Getting back to reality: As flying cars kept failing to materialize we kept thinking of them as an increasingly distant prospect. But if fully self driving cars are mainstream by 2020, it's not improbable that we might have flying cars mainstream by 2030. We've gotten so used to predictions of a dull future that an exciting one might just sneak up on us, and that is pretty wonderful to think about.