What i think we should bring to this game is a bit of diversity, otherwise in the end you just buy planes and find them routes:
Cargo and events are things that could be added, but in my opinion in a different way, there should be a "market" where you could buy contracts to deliver an amount of people or Cargo in a period of time ... for example you have the "October Fest in Munich " and in that time a lot of people will come from different places for a short stay so you could get contracts to transport those people (Charter type). Cargo the same thing without political restrictions you send your planes to the origin first and then complete the contract (3000000 tons from A to B in 20 days).
I don't even know if this is possible to be made in this game, and how much work it would give, I'm a zero in IT stuff ... but if you make 100 contracts that would repeat when finnished, it would be possible to work ... these are just "crazy ideas" that you guys eventually disagree or laugh about ... but thinking out of the box never harmed anybody !!!!
Nevertheless i agree with the ideas you are showing here, Facilities in your own terminals (Duty Free + catering ), The Hub system with people connecting is great if it would increase the numbers of pax willing to fly ( would allow the increase of planes in the small regional Routes for shure), a Fuel Market would be interesting !!!