I don't know if this has been suggested before. If it has been so, please feel free to ignore or delete.
What if alliance members could build/extend terminals in alliance hubs abroad. For example, two airports in different countries, both hubs of a single alliance, have exhausted all their available gates. Neither airline cannot add flights between the airports because they don't have gates available to them and they cannot build terminals abroad.
Is this a good idea? Is it hard to code? What if the hub closes or the airline drops out of the alliance, should the terminal be kept by the builder airline or demolished or gates turned over to airport management for lease to the public.