Private Jets and Private jet charter companies.
I would love to see the implementation of private jets and private jet companies, I understand that private aircraft can also be seen as the general aviation however I am more thinking jets privately owned by large companies or by extremely wealthy individuals. I believe that this should wake its way in AirportCEO as it would offer a 3rd type of income apart from General aviation and commercial aviation. this could be implemented with things such as a way for CEOs being able to drive to their private jets via the airport road entrance with their private vehicles instead of going through the main terminal. I am sure there is much more stuff that goes into private jets than what I have mentioned but I believe that this is a feature that would make sense especially for international airports or as a stepping stone between general aircraft and a full commercial airport.
Many airports in and around major cities often have a private jet hub that is generally located away from the main terminal, and all major cities need some sort of place where privately owned jets can land either this is implemented as part of an existing international airport or a separate airport entirely.