RE: Servo failover bellcrank.
Yes it works, not all the fail modes of a servo includes a locked burnt out motor.
About applying half the torque of a servo with mechanical disadvantage is unfortunately just plain wrong and a safety issue in r/c jet models. In fact, this can led to burning out motors, no matter how carefully you choose them. Not to mention about the pointless extra load in the electrical system.
About the extra mechanical points of failure doesn´t matter how careful you can tension a pulley, pivot, slider, whatever.. it is has two extra rotating points wich multiplies the slop on all the system, that could led to flutter wich is a major safety in r/c jets too.
Kind regards, Enrique
p.s. Here seems that your keyboard have a problem as it activates caps lock in some words.