I wonder how well they'd scale if they became wide-spread enough to actually be an alternative to ground-based transportation. Would there need to be a complicated air-traffic control network to prevent collisions? Would there be "flying roads" complete with their own traffic jams like in the jetsons? Would popular destinations have long queues of vehicles waiting for their turn to land on the helipad?
We already have an air-traffic control network to prevent collisions. It works pretty well, except for general aviation aircraft without TCAS flying under VFR near non-towered airports.
We already have flying roads to manage an orderly flow. Air traffic controllers will sometimes hold aircraft on the ground to prevent congestion and maintain the minimum safe separation intervals. At busy airports sometimes aircraft are forced to circle in the pattern several times waiting their turn to land.
I know that, but thats for a comparably small number of large aircraft landing at a single designated location. It wouldn't scale at all to a city-wide air taxi service.
It's not just for large aircraft. ATC manages flights to many smaller airports as well including charters and private aircraft. The system scales pretty well. There's no realistic prospect of having thousands of air taxis in flight at once above a single city, that's just never going to happen and not worth considering.