Funny you mention Hong Kong. It's where I live.
I don't see flying cars/buses/whatever here any time soon. The reason: high-rise buildings (most city blocks here are anywhere from 50 to 480 meters tall) and mountains (the tallest being over 900 meters tall). With those high-rises there is almost no place for any aircraft to land safely, it's just too dense. There's a heliport at the harbour and a few super luxury hotels have helipads on the rooftop. That are about your only realistic options.
Add to that the sheer volume of people that want to be moved. Trains are the more efficient way to go for that - the busiest line is operating 12-coach trains, 20 trains an hour, and it's actually not enough to handle rush hour traffic. The train network is being expanded steadily, with more lines being added. Mostly underground, out of the way of everything. Currently the trains handle some 3.5 million passenger trips every day, road public transport (buses, minibuses, taxis) handle at least that number of trips between them.
Other dense population centres will have the same problems. Huge numbers of people that want to move around, basically limiting any air transport to just a fancy premium service. No space to land on the ground as you're always too close to buildings, one of the main issues after noise would be the unpredictable winds tossing your drone around.