FWIW, we needed cut off switches on brake levers when bikes ran on brushed motors. Brushed controllers had a way of failing that resulted in full throttle to the motor.
Brushless, I suppose its possible to fail this way, but I never had it happen, nor heard of it. You could have a pair of wires to the throttle get cut, and short, resulting in a signal to full throttle the bike, but really,,, its not going to happen. Or a throttle could jam on in a crash I suppose. But again, about as rare as it happens on a motorcycle, which has a handlebar mounted kill switch.
So basically, you just need the same thing motorcycles have, mount that switch on a handlebar. Like motorcycle riders, you are able to not pull the throttle when you want to stop.
If you have PAS, then its another story, the kill switch will help you not activate motion when you fiddle with the pedals at a stop sign.