Two possible partial solutions to the problems caused by passengers who delay evacuations by taking items from the overhead lockers:
1) Recognise and allow for the propensity of passengers to reach for their hand luggage during an evacuation when determining the maximum number of occupants in a cabin. A benefit to passenger comfort, but not necessarily to airfares, could be a reduction in seat rows, with a corresponding increase in seat pitch.
2) Allow at least one hold bag on all fares and charge for anything more than minimal cabin baggage. Enforce the size rules rigorously, and demand payment at a high rate for anything too big that makes it to the gate.