Assuming this was not suggested before, It would be nice to add a Seating Pitch system in the future.
This would work by passengers choosing an airline with better seat pitch, legroom and or higher reputation. Less reputation and or Less space and legroom instead means less reputation. Instead of 550 slave ship 747 flying between JFK and LHR we can have a moderate 390 seat 747 or instead of a 189 seat 737-800 we can have a 160 seat 737. This would reduce the demand as having more seats can only be propitiable if you cost the price of a ticket less than a carrier with better seat pitch, and legroom. One of my airlines uses 130 seated 737-300s instead of 145 seated 737s. Which allows for more use on fewer routes.