I was thinking of a similar idea as well, but implementing it would be a huge challange. Though many FBW systems could have their FMC programmed with such scenarios, you would have to modify the A/C to be able to configure flaps/gear for landing even if it is CATIII certified. And that still leaves out the whole thousands of older A/C that don't offer any of these features.
I like the idea of placing some sort of chloroform/knock out gas system in the cabin that could be activated by the cockpit crew in the event of trouble; a few seconds to don your oxy mask and punch the button, within 10-20 seconds everyone is passed out. Divert to the nearest suitable field and by the time everyone wakes up, the cabin is filled with SWAT teams.
In addition, does anyone know if it would be possible to train cockpit crew in various types of high-G manouvers that could disable anyone who wasn't strapped in...i.e. a high-G split-S or Immelman that would throw anyone not strapped in to the back of the A/C and probably knock them out and/or break a few bones in the process. I don't know what the load limits are on a large airliner, but I'm under the impression that they're higher than most people in the cabin could stand. I've read numerous reports of FA's breaking ankles during encounters with clear air turbulence. Would not some crazy manouvering of the A/C have the force to disable anyone/thing not secured?