That was such a good idea that AA did it. There was a biiiiig advertising campaign about the extra 2 or 3 three inches leg room in Y.
As I understand it, about two years later they quietly started to reverse the process because they did NOT get zillions more folks buying their seats. They found that people ONLY want the lowest seat price. Then they moan about the seat pitch and swear never to fly with that carrier again. Next holiday/trip they look for whichever carrier has the cheapest seats ...
PAXboy, the mistake AA made was to apply this to ALL Y seats instead of introducing a premium product like UA. This seems to work well, it certainly does for me.