Chris Bangle had the idea that future cars will be fleet based, but people will own customizable interiors. These would deploy into the vehicle. You could also

Chris Bangle had the idea that future cars will be fleet based, but people will own customizable interiors. These would deploy into the vehicle. You could also have self-assembling cars - individual electric autonomous units of drivetrain. Two wheels and an axle - you call up as many as you'd like. While very future looking, I think these address both the ownership desire and the efficiency benefits.