I know this will be a major inconvenience, especially to business travelers, but how about banning carry-on bags (except for medicine, inhalers, and other medical equipment). This should also reduce boarding delays. Banning knives of all sizes is a good first step.
Also, security and screening prior to boarding needs to be updated. Identifying these people before boarding is critical. Once they are onboard, the crew is already
at a major disadvantage