In the 70s when a lot of this system was designed, the industry was selling 10x the number of GA planes it does today, so I imagine 10x more were flying as well. So we have the capability for an order of magnitude increase. We'll need more controllers, sure.

But, you are totally right, we need to move away from voice based ATC to more digital systems that allow a management of more aircraft, and allow the GA aircraft to manage themselves through a "peer to peer" type ATC system, but like we have with our cars.