At least one U.S. airline (I forget which) briefly used a transparent scheme to work around this: the first class rows were boarded first, and from there was back to front.
Maybe I haven't been paying attention, but I fly a few times a year and I thought this was how approximately every airline did things since roughly the dawn of time. They always start off with "first class, elite status members, families with small children, etc.", then once that phase is over they fill in from back to front.
