I grant this may be stretching things, but certainly in the Realistic Worlds could there be the ability for airports to open and close during the course of gameplay as in real life (Berlin Tempelhof is no more, and London Southend opened in this millennium); following on, for countries to come in and out of existence (collapse of the USSR, African countries emerging from the old empires etc)?
Also, I would like a facility where you could enter some parameters for what kind of aeroplane you need for your routes, and the game would suggest suitable planes.