Yep. Why should the cars be parked? Why should we own cars? All we actually need is a very high % chance of getting access to a car whenever needed. If it were 99.9%, and wayyy cheaper than owning a car, why own the car?
In the city, I couldn't possibly agree with this more. When I lived in Boston I sold my car after the first two years because it was a ridiculous expense and hassle for the utility. Taking a cab a few times a week turned out to be cheaper than parking tickets alone.
Given a choice though, I much prefer to live in less densely populated areas (e.g., northwest Montana), and owning a vehicle is really unavoidable. In these places that also means a 4x4 SUV or truck, not a Prius, or else you'd be calling a tow truck every 5 minutes in the winter.
I would expect driverless taxis to end up like public toilets.