The development of new in-game aircraft series
I suggest that airlines have the possibility to pay for the development of an in-game new airplane that serves the interests of the airline by paying huge amounts of money. The airplanes of course are going to be special. For example, my airline could pay for an ATR72-500 aircraft that has a higher range or that can carry a little more passengers. These aircraft can only be used by the airline that pays for their development and these are special aircraft to serve specific airports in a country.