Interesting concept but I suspect the regulators will see the role of the CC as evacuation only. In a LoCo B737, for example, where the cabin is served by as few as THREE CC (correct me if I'm wrong here) seems there's no room for anyone to be distracted from their primary task of evacuation to take the time to try and access the cockpit to shut down the engines - not if you want to get everyone out in 90sec or whatever it is.
Maybe it's different in the regionals where the door is close to the spinning prop blades and there's a better crew/pax ratio.
If the pilots need help shutting down, the a/c is probably in bad enough shape to have shut itself down without further action being taken...
