I don't know if this chain of events actually lines up. The way I see it, autonomous vehicles will allow anyone (not just millennials) to reclaim that lost time commuting, which can be used for work and thus make the idea of commuting from the suburbs not all that bad. Then people won't mind moving far away from the city centers given that the commute is no longer a fruitless activity. Personally I'd be very happy to live an hour away from a city if it meant that I could use the 2 hours round-trip to do work (if I still had to work in an office).