+1 - The real problem isn't boarding priority but enforcement of carry-on policy. Any bag which doesn't fit the sizer ought to be gate-checked to the baggage office at the final destination where it can be collected after paying the baggage fee + hefty penalty (no freebie luggage).
While it's true that if ever pax brings a roll-a-board + personal item, the OH will still fill, not every pax does. Certainly the OH won't fill with 50% of the aircraft.
There are ways to deal with bad pax behavior and this is one. The DYKWHIA's who don't know how to measure a bag or pack, can stand in line at arrival while those who can read and count are already in their room at the hotel.
No muss. No fuss. No gate lice. And, just like the old days, FC can board last if it chooses so that high-fare pax spend the least time.