Safta's sim and Colgan 3407 both seem to involve the autopilots having the AC in extreme trim before stick shaker. Presumably the AP "knows" when it is having to going to extreme trim, is an opportunity for a warning being missed? What should the trim threshold be? Should it be selected at a point at which an attempt at full power recovery might increase the stall? Or are extreme trims too normal for warnings to be anything other than distracting?
Perhaps it would be better for the A/P to run out of available trim and allow the a/c to descend below cleared altitude or g/s or selected v/s than allowing trim to be at a point where full power will result in an uncontrollable pitchup to stall.
There are of course problems inherent in allowing an uncommanded descent, CFIT and traffic conflicts come immediately to mind.
I suspect the certification authorities will be revisiting these issues.