i think they should set a 8kg limit on the carry-on luggage, max of 1 piece per person regardless of class. anything heavier than that automatically gets gate-checked.

this would make it fair to everyone on the plane since bin space is shared by all and the weight limit would probably lend itself to people using smaller carryons especially wheeled bags.

allowing those people w/o carryons to board first isn't going to free-up more bin space nor discourage those who try to bring their bags onboard to avoid checked fees.