Now before I begin, I know this is a HUGE task for FDS. I also know that their will be a HUGE increase in realism with this - and I’m sure that my IFATC friends would love this to be implemented.
My suggestion is this - Radar. At the moment, ATC have the hugely unrealistic gods gift view of seeing everything that is in the skies in their region, and I suspect the world come Global.. Within TS1 this is mega annoying with random tower controllers requesting you contact their frequency when you’re 50+nm away and way out of their Air Traffic Zone.
In the real world, a great number of airports use a Watchman Radar with a range of somewhere in the region of 40nm (can be 50 on a good day). So what if you chose an airport to control, and boom - that’s he ONLY radar you can use? Area control would have it different and be able to select radars in the area they’re controlling - here’s the catch, area radars have a detection range of around 250nm. Tactically placed around countries all over the world, these radars provide truly insane coverage.
If you need more info, let me know - I’ll try to make it less confusing!
Also, if you’re interested in the history of radar then PM me and I’ll be more than willing to discuss it :)