I know this has been buried for a bit, but just wanted to say I see this as a great use case for machine learning. The big data points would be real-world transcripts from control comms, transponder/gps data, weather, and charts. I don't think any are hard to get given the online resources that dish them up for free.
I'm thinking a machine watching an airport with tons of traffic (LAX for example) for a couple months worth of data and a human babysitter could do the trick. Do the same thing with enough airports, small and large, and you could feasibly start applying realistic ATC to airports without any prior training for that location...
The way I'd handle real-world traffic, is when an aircraft enters controlled airspace, it gets handed to the ai controller, which should in theory direct traffic much like a real-life controller would, because its already studied gazillions of real-life situations. Pretty much how Testla is teaching their vehicles autonomous navigation.
Someone mentioned different traffic handling depending on congestion, and it would do that. Same with weather conditions and any other real-life scenario it could observe through data.
It would be a huge undertaking, but given unlimited resources, budget, and computational power (cloud), its how I'd approach it.