Hi!
Another suggestion:
When making island hopping routes (e.g. Hawaii or the Caribbean), the prices need to be low because of the small distances, therefore reducing profit. If each airport gets an island attached, you can get a lf bonus when flying short routes to nearby islands. If there is more than one airport on an island, they would share that island and routes between those two airports won't get a bonus.
Just a short thought, what do you think?