"You're better off just renting a car"
I think this pretty much hits the nail on the head. Why own a car that sits unused for 90%-99% of the time? When all cars drive themselves (as seems not only possible but entirely practical in the early 21st century), I can foresee the ability to book a car online, have it pick you up and then deposit you at you destination for a fraction of today's cab fare. The economics appear to make so much sense. Also, with self-driving, possibly networked cars, you'd go a long way towards eliminating traffic problems that plague most car commuters on a daily basis.
May be the cars won't be rented, maybe they'll be shared between people or something, but as soon as people realise they don't have to pay to a fortune to buy, then maintain and fuel their vehicle, I think the economics will speak for themselves.
Ah well, I can dream...