do you have any warning light output from the calipers? What happens if the driver doesn't fully release it and goes for a long drive?
Ohh, i've seen the results of this haha.
Back when I was silly enough to turn spanners for everyone else, We had a bunch of Mercedes Sprinter vans come into the workshop for a recall, They were retrofitted into ambulances for the Victorian Ambulance Service. The outfit that did the retrofit managed to disconnect the handbrake warning light on the dash of every single one they did, so we got the recall job to fix the wiring problem and replace the rear brake rotors and handbrake shoes. The paramedics would often forget to disengage the handbrake all the way because it was located so low on the floor, It actually took leaning sideways on the seat to really put it down. The engine was plenty strong enough to overpower the handbrake and they'd drive away, the shoes inside the drum would burn out and cook the rotors. The worst one we had got so damn hot it actually split the disc from the rotor hat, Boom, no more rear brakes and a fully floating rotor.
A tourquey electric motor should have no problems at all overpowering the handbrake...