Unfortunately the CPSC warning is too vague to know if this is people pushing the device past its documented limits or the device failing within the standard limits.
Yes, agree with you both - probability * severity. The severity is high (unless you know how to run off the board - that lowers the severity quite a bit). The probability is unfortunately unknown.
I assume you mean the board fully power off while riding?
If yes, then no.
It is possible to overload the motor by going over the maximum speed or going uphill by at too high of a speed but in that case the board will not actually power off.
The only way the board may turn off is if is fully charged and you immediately ride it downhill (regenerative breaking). To protect the battery from overcharging the board it will turn off in that case but the app will warn you before that happens and for newer boards they have implemented the ability to charge to less than 100% if that is how you start your route.
This is a cool project, but I would more concerned that replying to spammers confirms you are real and that could result in much more spam. So is the net increase in pain your own?