As a 50k who's over 6', if I'm sitting in Y I want to be in a preferred seat, so I'd much rather just have the 50% discount and have a greater chance at actually getting one of the seats. As Cow rightly points out, there just aren't enough preferred seats on the widebodies for this to work. Unless of course they want to remove a row of regular Y and use the space to make 7 or 8 rows of preferred seats, but somehow I don't see that happening!