If a few aeroplanes are lost because of the operation of that killer switch at the wrong time then what? This cure may prove deadlier than the disease.
As there is extensive experience with FBW planes that have a pilot override we could actually use that experience. As far as i'm aware there was no 777 incident because of that, unlike airbus where a few incidents have happened due to hard protections (bilbao, lufthansa, qantas etc).
However, given the extremely low number of incidents caused by the hard protections there is probably no regulatory need to change anything and apparently the insurance companies are quite happy as it is as well, otherwise they would require higher premiums.