Just as a reminder free flight was an alternative to IFR control proposed a couple of decades ago that would put instrumentation in airplane cockpits allowing them to know where other airplanes are and have the pilots resolve the conflicts themselves without controllers. If I remember right, busy airports would still have controllers and sequencing, but en-route would be up to the pilots involved.

I'm surprised with the talk once again of privatizing ATC and the deployment of ADS-B that this hasn't been talked about more. A much more limited ATC that was privatized would be a lot less scary than giving a single private organization ownership of the whole sky.

I can see training issues as well as system issues, particularly given the need for UAT to 1090 repeaters causing difficulty in seeing all traffic close to the surface) But the biggest problem may be resistance to change which seemed like what killed the idea las time.