I have wondered if this was a valid option scientifically. Its my understanding that the most advanced bionic arms use nerves that run to the shoulder and then attach as controls for the arm. If that is what was done, it seems that it would be no good for ALS because these are the very nerves that are destroyed by ALS.

However, there are more advanced "brain control" devices that have been experimented with that feed directly from the brain. If they can get THOSE to control an arm (or leg!) with accuracy I would say, "lop em off". They can call me the "Six Million Dollar Wayne"