You make a good point here. Future transport system will have to leverage existing infrastructure to be successful. Multi-modal transport, like you are proposing, has are not easily solved. The time required to switch from one system of transportation to another requires hubs and introduces bottle necks and very advanced planning, perhaps even magical foresight, in regards to developing areas. A unified, personal transport system can scale more easily and has the benefits of privacy. That's why cars are relatively successful and haven't been replaced yet.

I'm unconvinced that collective transportation is the real solution to the problem, but it is the best intermediate solution we have right now. Downsizing cars, removing manual control, unifying speed, and adding distributed routing capabilities seems much more promising to me.