What about special seals for the baggage compartments? Similar to the ones used for catering trolleys, but much stronger? Mechanical locks would need approval, be expensive, etc, but this sort of seal would be very cheap and easy to approve.
The hat rack could have 2 holes (easy to add to existing AC) where the seals would go though, these seals would have a large band hanging from them with stripes on it or something signaling the hat rack is locked. Time-permitting, the pax could be allowed 2 mins before the cabin is secure to get their precious passports and Ipads from their bags and after that the bags would go to the luggage compartment that would be sealed straight away. So now everyone has their precious sh*t with them and they know that the compartments are sealed and not to be touched.
Plus if someone would try to force the compartment on ground, the guy standing behind would definitely push the idiot and no bag would be retrieved, the other pax wouldn't see any bags coming out and wouldn't try to get theirs.
Seriously, how difficult is this to implement?