Honestly, I do not believe it would be that much of a problem to make it possible to fly the aircraft from the ground in cases of emergency. Especially not in A/Cs with FADEX, FBW and so on. Of course it would cost money and might open up oter security problems as described above.
I think it is a question of:
- do we want that?
- do we want to invest the money?
- how big is the additional security risk?
But what about a fail safe button like on trains?
If the pilot does not press a butten every ten minutes (just for example) the A/C holds automatically. Perhaps even in connection with the oxygen.
If there is no steering input at all after some time of the deployment of the masks, the cockpit door unlocks automatically, alarms ATC (via Mode S)....
Would that be a way?
Regards, Bernhard