IMHO I think like most things it starts in commercial service in very subtle ways. But autonomous vehicles are fully road legal in Nevada for instance:
Yes, the regulations say that you have to be present in the car with two drivers right now, but they're very easy to understand, and you can see that all they have to really do is strike 482A.130 and bam you can have cars on the roads with no drivers completely legally:
But I don't think that happens short term.
Commercial trucking is where this is really going to start IMHO - it'll be like autopilot for planes. Driver teams will be able to operate a truck continuously for 24 hours a day without stopping. One will sleep, one will have "control" of the truck if anything goes wrong. Once it becomes more accepted, then drivers will gradually be able to become more "hands free".
But that's just IMHO.
To me the autonomous thing makes complete sense - car enthusiasts will always have cars they can drive themselves, but I think the economics of shared ownership (or renting per hour/day) make a lot more sense for a lot of people as cars are very expensive and rapidly depreciating assets that sit idle for the vast majority of the day. Autonomous vehicles will help drive the cost of shared ownership/rental way down, and will give an alternative to ownership for those that want to be able to go anywhere, anytime.
Like anything, it won't happen overnight, and it probably won't happen in quite the way we think!