I like your point that without personal ownership we would need fewer cars and built infrastructure. Never thought of that.
I think the hardest part is getting the price down. Driverless cars would first replace taxis, which means their business model will require charging a similar amount. Once they become dominant, the price will not come down. The only way it would is if the whole fleet is owned by the city rather than private companies - also unlikely.
I'm looking forward to this reality, though.