Huh? I've yet to see any carrier that has full premium economy cabin allow folks who have booked standard economy to move into premium economy just because they don't like the look of the remaining un allocated Y seats... Just because UA doesn't have a wall between E+ and E- and because UA choses to put folks in E+ for free should they have too many in E-, doesn't make things different... It's a "premium" product which UA have a right to charge for, and if passengers want to guarantee they get it they should either pay the fee for it or conspire to be in one of the groups eligible to get it for free.