Long shot, but I think the following list should be included.
Departure frequency: This would perhaps be a good way to incorporate SIDs/Stars into airports and should have the option to be toggled off and on for multiplayer usage, smaller airport usage, and just psychotic behavior. The purpose of it would be to direct VFR traffic for touch-and-gos, delegate and set up proper arrivals for incoming traffic, and maintain the separation of aircraft for outgoing and incoming traffic.
Delivery: This could be a fun role for multiplayer games, adding an extra slot that goes over flight plans, delegates squawk codes, and perhaps departure routes and runways.
Ability to add more roles in Multiplayer