Not true. If end gcode turns off the Z stepper enables, the bed’s going to crash unless you use the stepper enable line to act as a BRAKE_DISABLE for the logic tree. There’s probably other edge cases where this could happen, like in Klipper as described here:
It’s not just about preventing back EMF from overvolting a board power rail. Shorting the coils also supplies holding torque at the steppers which will slow down or even stop the drop of a print bed or a lowrider gantry.
Ideally: Short coil A to itself (only) and short coil B to itself (only). Motor power or driver enable must be removed from the stepper drivers before this or they will go into overcurrent (best case) or cook (worst case).
I haven’t given up on the idea of a pass-through protective carrier, maybe with a cheap but effective SCR e-brake as was discussed. Just no time to work on that idea at the moment.