I believe that releasing AE4 as a huge package of new updates rather as small updates one at a time isn't the solution for Airline-Empires.
Firstly, players will be shocked by the sudden change of game mechanics. Things may be in chaos for a while after a huge update, and I mean for a long while. Eventually, people will have to play more realistically. However, a bug-full AE4 would be a nightmare, as the coders would have to find all the glitches that are in the system while there are a million updates to everything.
Secondly, releasing AE4 as a set of updates rather than a package will prevent the coders of the game from prolonging the finish date for AE4 as players keep wanting more features. I recommend that the coders of the game would release features in the following order, from most impacting gameplay to least:
-Role-Based Airline Management (this would set in the place the foundation for the rest of the updates. Players in a role would concentrate on certain parts of the airline, as you said in your topic about the said update, and players could also have a simplified version if working by themselves.)
-Fluctuating fuel costs (this will kill a LOT of the airlines operating Soviet-era planes. Also, this update would greatly increase the need for aircraft efficiency. Fuel costs could be real-life or made-up.)
-Real Connecting Pax (I'm assuming that this is one of the harder updates to do. The release of real connecting pax would suddenly a magnitude of airline types to be viable, mostly being the types reliant on the hub-and-spoke model, and would greatly enhance gameplay.)
-Airline Hours Pooling...
And so on.
I will add to this.