I thought a bit about this and wondered whether a passenger in F should be charged money to have a meal sold in Y. If the options in first are not desirable, should FC passengers have a choice (up to a set monetary limit) to pick something from the Y menu? What if the Y offering (one day) becomes more appealing than FC? I suspect people would feel strongly one way or the other.
United allows F passengers to eat from the Y menu free of charge. CO charges for the stirrings mixers. Unfortunately, rumor has it that $mi$ek may force UA to do the CO thing of charging F passengers for all sorts of "extras"