of course, in real life airports grow. and that data will find its way into airline sim, thus airports will be updated and "grow".
Exatly. And the suggestion would break that fixed, rigid frame in a subtle way.
AS can only try to copy real life. You can build the largest hubs only around existing, big hubs, because that's where AS has the biggest demand/capacities.
As a simulation, the world should also adapt in some way to the game play. That means, if somebody manages to create a big hub on a (real life) medium size hub, why should it not be possible to have that specific airport extended in the game, as apparently the player manages it very well.
On another point. Yes, we all would love to see the use of widebodies on a heavily demanded route. In real life, that happens sometimes, but not too often, although no airline will fly 50x a day with a LET. But let's assume, we can trim the game play to favor the use of widebodies, that some players will switch their aircraft (given they find the necessary slots on the already congested airport, due to different TA-times). Now will a big player release the slots to others? Most likely not. He will be prepared, and fill the empty slots with new machines to new destinations. Just like in real life. If BA uses 2 A380 instead of 3 777 to a destination, they surely will not give up the slot, they will fill it immediately with another flight for their own expansion.
My argument is, whenever an airport is full, it will stay full, no matter what. Once the limit is reached, it will become static. No gameplay takes place anymore. It simply stops. The expansion of the airport would trigger new activity. It will enable the big, as well as the small player to do something new. And I'm convinced, that many players would be able to take advantage of a new runway, not just the big fat cat dominating that airport. Let's assume, I build a new runway in Beijing, so that I can grow further. Other big players will now suddenly have the chance to schedule additional (or even for the first time) a flight to that destination, because previously it wasn't possible. Or they could add a second daily flight. It would help to increase their network, and enrich their game play. Yes, the dominating player of that airport would probably benefit most, but he's most likely also the one to invest the money.