I like the idea of a regulated north America with an all out free for all in 82!!
It could be "interesting".
Routes limited to a capacity of 150% of demand would force a total rethink in how you order and allocate aircraft. Using a 300-seat demand trunk route as an example (Say LAX-Chicago), when you are limited to a TOTAL of 450 seats of capacity, divided by 4 eligible airlines, that means you get just 113 seats, regardless of what anyone else is doing.
Do you throw ALL of those seats on just one aircraft? Or do you run two smaller aircraft for the competitive advantage? (Since all airlines were fare-controlled by the government with ony inflation adjustments allowed, the competitive differences were SEATING, and the level of inflight service, such as meals, drinks, sky hostess skirt lengths, etc)
You are also competing against the Whistle-stoppers who are not bound by the 150% route limit, but rather by the limit set by the routes they are stopping over at.
Say they run LAX-FSD-ORD:
The MAX number of seats they can run into ORD on that route is 150% of the demand on LAX-FSD, or FSD-ORD. They could run a DC-6 or a 727 over the route, but they would be limited to just the 80 FSD-LAX seats, and then 45 seats into ORD. That means they could only offer 45 seats LAX-ORD.
And they can run any number of flights over different cities from LAX-ORD, with the stop-over penalty, of course. Until 1979, you are all charging the exact same fare for it.
If you want to complicate things even further, you can add the CAB's route bidding system in, as well. (Minus the "Juan Trippe Method" of buying Senators, of course.)
In the beginning, you BID for the rights to fly a route. (Say, starting at the slot cost as a minimum bid.)
Any number of airlines with a hub at either end can bid for the non-stop rights, but it will be awarded only to the highest bidders.
When a company goes bankrupt, the route, or their portion of it, becomes available for bidding again, with the award coming 90 days after the bid deadline.
To add some poison, if you are awarded a route, you MUST fly it within 60 days, for at least two years, even at a loss. if you don't fly it at ALL times (Even during D Checks) you get fined by the CAB, heavily.
You will REALLY have to think about about where you fly, how you bid, and what you buy/lease. You won't be able to simply buy up all of the aircraft production, and simply plaster the map with flights.