awblain,
Circuit breaker design isn't going to stop a deranged crew, or fraction thereof, of going postal.
No, of course, but they may think twice if they know they can be traced.
My post was actually partly inspired by a BEA study post-AF447 investigation, referred to somewhere in the early part of this thread. It had a slightly different theme - the scope was to detect when the airplane is doing unusual maneuvers (as AF447 did) and then communicate relevant alert messages over ACARS satcom.
So the main intention was the same - to ASAP inform the outside world that something unusual was happening to the plane, with some details (such as position)
I don't know what has been the result of the BEA study, which recommended implementation in aircraft getting certified in 2018 and in legacy aircraft by 2020 IIRC. I thought it notable in this context anyway.
Linking to the legacy equipment hardware is of course slightly more difficult than linking to the flight instruments (which presumably are already connected to ACARS in most a/c types) as in the BEA study. But there may be some easy wins, especially for future airplane designs.