I'm not sure how feasable AI or automation is. How would you respond to a failure in the automated system once there are more planes in the air than ATC controllers in that area? That could be a single point of failure. ATC Can optimise for severe degradation of service but how would automation be able to respond to a sometimes unavoidable impossible situation?

You can define rules how planes should and shouldn't fly, verifying that this is always possible would be a nightmare.