The only problem I see with the solution of cars, insurance and fuel hopefully getting cheaper, is that it's based upon a significant drop in demand (ergo supply rises, then prices drop, cars become more accessible, popularity rises again, presumably).
Apart from the problematic assumptions there, for US demand to reach the levels it would need for those assumptions to occur, most Americans would have to use public transport for most of their travel.
This could be viable, but the US population is too spread out and too many local governments could care less about public transport. For comparisons, US population density is more like Eastern Europe than Germany or France. Light rail, etc. works in those places because virtually everyone lives close by, in Eastern Europe, cars are way more necessary because people are more spread out.
In my mind, the most dangerous thing about this whole teens not interested in driving bit, is that manufacturers might continue to chase the younger market and all new vehicles will just be terrible because manufacturers just make overly mpg-conscious, droll vehicles with tons of tech stuffed into them.