It’d be far better to just connect the B- to the VESC power with a high-current wire (as we do now) and connect the BMS’s P- to the VESC with a small current wire.
When the BMS cuts power to P- then the VESC could see this and cut power slowly until off, but leave braking enabled.
This would ensure the BMS was still responsible for managing the battery, by itself, no matter how many VESCs were connected, and ensure that the large currents were still bypassing the BMS.
It’d be win-win-win. Let the BMS manage the battery, but send the signal that somthing is amiss to the ESC. From a port that the BMS already has for this purpose.
Kind-of like this, but with the VESC able to see if the lights are on or not, and cut throttle if not.