Thanks a lot for your elaborate feedback, everyone. Really appreciate it!
Since I can literally smell the fear in the room, let me a get a few basic things addressed first.
Firstly, and as mentioned in the OP, this is a “conceptional topic”. What I mean by that is quite literally that the goal of the roadmap item is to come up with a concept for this part of the game. It’s an initial vision/idea for what this might entail, but nothing concrete. So everything goes.
Secondly, the goal isn’t to drift into “AirportSim”, but quite the opposite. The current system is sort of a (bad) airport simulation, as we have airlines building mini-terminals left and right, which makes no sense, has no equivalent in reality and adds very little to the game besides cost-savings and a potential quality bonus.
Thirdly, I am not planning to add direct operational features to the game. All of this relies heavily on the assumption that some sort of more or less powerful Auto-Ops feature has been implemented that allows players to address operational issues on a strategic/tactical level without having to mess with day-to-day ops manually.
Lastly, I am in fact considering removing the current style of “building own terminals” in favor of a more passive “petition the airport to expand” kind of feature. But as said, nothing is set in stone. It’s all just vague ideas at this point.
That said, this feature has to be seen in the context of the overarching design goal of most of the things on the roadmap: To enable airlines to actually follow different strategies and business models, rather than the current “make numbers go up” model that has all airlines competing for the same 4 passenger/cargo types within a framework that - at the end of the day - is utterly static and shallow.
@rubiohiguey2000 This is not meant as criticism, but just as a really good example for what I mean by the above paragraph: Look at your airline empire in Idlewild. The parent holding alone operates nearly 4000 aircraft, I didn’t even check the subsidiaries. Even the very largest airlines in the real-world don’t get close to this. And this of course explains the reaction to my suggestion: When I take a step back, read what you suggested and translate it to the core meaning, it reads like “you can change all you want but make sure to add features that ensure nothing changes”. You even state that you want a single-click feature to ensure you to “handle everything at 100% satisfaction”. And this makes perfect sense…in current-generation AirlineSim, this probably is a sensible request, as “100% satisfaction” is the only thing that works.
But that’s not how the real world works 
The real world is about trade-offs. Everywhere. Ryanair operates our of HHN because it’s small, it’s fast, it’s cheap. Lufthansa operates out of FRA because it allows them to operate an international hub, despite (or because of) the higher costs, longer turnarounds and possibly lower passenger satisfaction. In the future, I want these things to matter in AirlineSim as well. I want players to have to make explicit choices about how and where they operate and why.
Is this going to be more difficult? Probably. Is it going to be more engaging and fun? I’d hope so 
What I really hope won’t work anymore is the “just add more flights” type of mega-airline we have today, where the size of an organisation simply doesn’t matter and one can just grow to whatever physical limit there is. Obviously, this is a long-term goal and a lot of pieces have to fall into place to actually make it work, but I hope you get the idea.