I agree that airlines play the divide-and-conquer game a lot. When they first introduced these fees I predicted correctly that they'd get a public-relations black eye at some point for breaking up families, so that's a possible lever if seeking regulatory or legislative action.

A key domino with this one will be Southwest. They already have an unusual and timeworn seating procedure (that they'll let people jump to the line of for a fee). They're no doubt under pressure from Wall Street to go to the dark side on this and on bag fees.