> Wouldn't some of the higher-risk demographics (e.g. the elderly)
Elderly aren't usually considered higher risk. The young kids are, enthusiasts are, people who drive red sports cars are.
> Unless a critical mass switches to car-sharing, autonomous cars and no parking will make rush hour worse because now each car will make the round trip to work twice a day instead of just once.
Autonomous cars should be mostly fleet vehicles (otherwise you have to park it at home).
Isn't that just like in most of the major world cities where taxis are the norm rather than the exception? It isn't weird for a taxi in Beijing to make 5-6 morning commute rounds. But even then, there are a lot of reverse commutes to consider.
> The financially sound thing to do will probably be converting these lots to more offices/condos/malls.
While density can increase, convenient affordable personal transportation also allows the opposite to occur. Parks, nice places, and niche destinations, are also possible.
Think of it this way, once traffic is mitigated, urban planning can apply more balance to eliminate uneven reverse commute problems. There will still be an incentive to not move, but movement in itself wouldn't be that expensive (only 40 kuai to get to work in Beijing ~15km, I'm sure given the negligible labor costs, autonomous cars can manage that in the states).