...until the people who are boarding first throw their bags into the first available overhead bin. Not a problem when loading from a second door (such as on the 757) but definitely a recipie for some extremely irritated first-class passengers on Airbus and 737 equipment when they find zero overhead space in the first half of the plane.

This would also slow down the deplaning process as well, as the passengers seated up front have to either sit and wait patiently for those seated behind them to exit the plane (probability: zero) or fight through those in the aisle to move back in the plane to get their bags.

These would obviously be non-issues of passengers used only the overhead bins directly above their seats, but short of flight attendants being issued cattle prods, I don't see that happening.