The following is multiple feature requests all revolving around aspects of airports (lounges, gates, etc.).
Lounges: My first feature request are lounges. Lounges in airports would work similar to how terminals work currently. There would be a separate list underneath the list of terminals, for lounges. Lounges can be customized with selection of services included, what classes can be allowed in, capacity, and other options, to give a price, like the price given for airplanes based on engine selection, configuration, etc.
Gates: There should be a custom amount of gates at every airport to make it more realistic in size/capacity. We can't make gates to have a loading capacity and a list of lights compatible to board on that gate, so the easiest way to make this feature would just to be consider all of the gates to be of the same type. Terminals should also be a feature to make it even more realistic.
Subsidiaries: Not a feature that is necessarily needed, but subsidiaries would be a cool feature.
Sponsoring: Like subsidiaries, not a feature that is necessarily needed, but sponsoring would also be a cool feature. Airlines would be able to sponsor numerous companies.
I know sviridot is very busy with work and would probably be unable to spare the time for the research into most features these days, so my suggestion is that active people in the community, if he approves, would be able to compile a list of, for example, gate counts for major airports worldwide. If there is interest from sviridot after seeing a sample of the data that would be collected, he could approve a continuation and this job of collecting statistics could go on so that, in example, gate counts could be listed for most airports that exist worldwide. After that, all sviridot would have to do is add the feature, which will take some time, but not as much as having to research beforehand himself.