What would happen if feds cap airline change fees?

Once upon a time you bought a plane ticket from point A to point B and it included a seat assignment (unless you were on Southwest), luggage (checked or on-board), and maybe even a snack or meal.  Now everything has been unbundled, with separate charges for seats, luggage, priority boarding and so much more.

Congress is considering an intervention by capping the amount airlines can charge for changing a flight reservation.  Currently American, Delta and United all charge $200 to change a reservation for a domestic flight.  According to WSJ, US airlines collected $2.9b in change fees last year.

What would happen if Congress put an upper limit of, say, $150 on change fees?  Standard economic analysis would interpret this as a price ceiling that would have unintended side-effects.  Airlines have already warned that they would raise fares and other fees in response, along with making fewer tickets changeable.  They also point out that customers who want more flexibility can pay for it when they buy their ticket by paying a higher fare.

But here's another thought.  The US domestic airline market is now very far from the competitive ideal of economics textbooks.  Price ceilings imposed on monopolists lead to lower prices AND increased output as long as the price provides a competitive rate of return.

My take: passengers and airlines have both benefitted from airline deregulation in the late 1970s.  Fares are much lower, more planes are flying and those planes are full.  What would really help customers is more competition.  What if we let foreign airlines provide domestic service?