Couple of suggestions:

1. Sudden events that place the player in a stressful situation for example: sick in a plane, injured person on board during turbulence,engine fire or sudden fog in the aircraft, aircraft malfunction, emergency landing of a plane that was not scheduled to land at that airport. It would be also cool to see sudden engine malfunctioning after the plane takes off and it needs to land immediately at the airport.

2. Airplanes that are more important like presidencial aircraft or private planes.

3. It would be cool to see that the wind affects the aircraft causing them to sway during landing forcing them to adjust to the wind

4. Weather conditions that hinder aircraft landing and takeoff for example fog or thunderstorm

5. Fuel system that acctivates when the plane circles over the airport for too long

6. The sound of the aircraft could be louder and audible from when the engine is started even during taxing

7. We should really see the difference during takeoff and landing with different planes and bigger planes need more runway.

I really hope to see some of it in the actual realese of that game because it has potencial and even the demo version is really good.