I don't agree that a locking mechanism will work. You'll just get lots of morons frantically trying to open the lockers to get their stuff even if it's locked.
I think a simply reminder just before every take off and then once again just before landing. Perhaps making it an offence would work.
Something needs to be done otherwise we might as well ignore everything we learned post British Airtours in Manchester. We might as well narrow the aisles, cram more in, deactivate doors and make partitions and door areas smaller if we are just going to allow people to haul their tonne weight hold-alls out in an emergency without any consequences.
Another Manchester will occur at this rate. Let's not let those lost die in vain or all the improvements go to waste.
Those who claim to need to take their bags for medication should place their medication on their person. This argument doesn't wash with me. After all, no airline guarantees your cabin bag will be stored in the cabin. There's a risk it will be offloaded. If so, what would you do then for medication?