Hi, I have the same intention and started to look into doing this, but have been busy since I got my machine.
The BMS is a “Daly” one, it has quite a comprehensive manual and there is already serial data being sent out for the Bluetooth dongle.
This could be picked up with an extra line to the handle, it would need a second UART RX pin to accept the data, parse it and check the cell voltages. There is also an “alarm” bit in the BMS data so the actual threshold could still be adjusted using that interface.
Anyway then the handle should warn the pilot early enough (it should be able to do this based on Ah discharged) and then buzz the handle and finally start to reduce the motor power as the lowest cell hits the limit.
Once that is done I wanted to reconnect the ESC directly to the pack (with a fuse), instead of through the BMS FETs.
What I need to find next is the schematic for the current handle version - I didn’t see it in the GitHub.