And someone has just launched the same discussion, again, in Tech Log.
I must say it does seem odd that the Airbuses have been flying for all this time, evidently, with an FBW system that in certain - extreme but possible - circumstances would push the nose down further and further with no way for the pilot to regain control unless he/she knew the fix of turning off 2 ADRs, which has only recently been promulgated.
But I suspect that's an over-simplification.