I have a suggestion for future versions of AE that I believe should be implemented, if possible or not already in your plans.
Political restrictions in game worlds are based on around 2010 or so. I would like to see restrictions and other aspects of the game change based on the date in game. For example, I run an airline in Ukraine, and two of my hubs are at Donetsk and Simferopol. Earlier this year, Simferopol became part of Russia, and Donetsk Airport was destroyed. For this specific example, around the time this happens in game, I should lose those airports as destinations. (And if you plan to make aircraft more dynamic, I should lose some at each airport due to destruction of them/possibly seizure.)
As another example, airlines in the Soviet Union should be limited to the Soviet Union/allies, neutral countries, and Western airports that were allowed service to the Soviet Union until each Soviet republic's independence date. On that note, I think there should also be a restriction on aircraft types. For example, prior to independence (~1991), Soviet airlines should not be able to buy Western aircraft, and Western airlines should not be able to purchase Soviet/Russian aircraft to the same date (maybe longer, since to date the only Western airline operating a Russian aircraft is Mexico's Interjet. I'm not sure if there's a political reason for that or not, however.)
I could list multiple other valid and important historical examples here, and for that reason I think this is important enough to be considered for addition to AE 4. This would allow for more realism in the game and I believe would make the game a lot more interesting.