I thought it would be very cool to implement hangers into the airport. Smaller hangers that could be bought by GA aircraft for a price set by the airport, the aircraft would return to its hanger every night. Medium and Large hangers would be available for airlines, these would be built and contracts would be put in place for x amount of years. They would be able to park aircraft and do maintenance on them here whenever they please.
Airlines also have rooms in airports that are used more multiple things. Mainly they are pilot preflight briefing rooms, offices, etc. If an airline has a good reputation with the airport it may lease these rooms for x amount of years.
Also, the pilot, cabin crew and airline executive NPCs could be implemented as well.