Neville-Nobody
For the record I'm not saying it can't be done I'm saying that the staus quo with some better techonology is probably the safest and most cost effective for now. I don't think full autonomy in pax aircraft will be happening anytime before 2090
Glad you are not saying it cannot be done - because it has been done. There are multitudes of autonomous aircraft, indeed almost all UAS are _required_ to be autonomous so that they can safely recover in case of a command link failure. Even the little octocopter toys will go back whence they came when they sense low battery.
Automating ATC?
Yes that is being done too - there are many simulators that will 'control' multiple simulated aircraft. Indeed they will happily run the entire FABEC or New York Metroplex at a few hundred times normal speed with 50% more traffic.
But you should always use the adage:
Just because you can, doesn't mean you should.
The easiest to automate is the aircraft, mainly because much is already automated. The adherence to SOP to the extent that what used to be finely judged decisions are now 'no brainer' SOP box ticking makes automation even easier.
Air Traffic Management is a larger problem and while flying aircraft around a scripted pattern can work well, each 'sector' interfaces with other sectors, the multiple sectors form groups with centres/centers and interface with multiple airports. The Air Navigation Service Providers or Functional Airspace Blocks interface with others and decisions made in one area can rapidly impact others. So while in small areas ATC can be run by simulators it rapidly grows into an Np problem as more areas are added and the cross impact of multiple trajectories are taken into account. That does not prevent several areas of ATM being given 'Decision Support' tools especially in conflict detection and resolution.
Importantly, the new ATM systems use the aircraft intelligence so that the aircraft now provides earliest time/latest time of crossing of waypoints or arrival, and the trajectory description used by the ATM systems will in the future be the one generated by the FMC not one generated on the ground. As more airspace becomes 'free route' that is everyone flying their business or mission trajectory the airspace will become more efficient for the aircraft and the airspace utilization will increase.
So there will be a lot of automation, I expect UAS to be just other aircraft in the airspace and from the system point of view there will be no difference in handling between piloted, remotely piloted and autonomous. It is a commercial/safety decision not a technical decision whether the Airbus 390 or the Boeing 797 will be optionally manned or not. But there will be unmanned autonomous aircraft flying in normal class A airspace. There already are to some extent.