Some airlines build up very large balances over time due to lulls in reinvestment periods (new ac not needed at that time, no new infrastructure (bases), etc)
It would be nice to be able to add an additional source of income by having the ability to do player to player loans based on the in game interest rates. There could be restrictions of course to protect both parties like only allow loans when security interest (aircraft) can act as collateral or limit the amount and terms when alliance partnerships exist.
I understand it can’t be as simple as what I describe but that can just be a start and a system can be developed.