I encourage any i3 driver reading this to try the following experiment: on an appropriately vacant road, drive at a suitable rate of speed and while maintaining that speed with the accelerator pedal, use your left foot to lightly brake, then moderately brake, then heavily brake.
You'll easily identify the braking force (possibly pedal position) threshold where power is cut to the motor, no matter how hard you stomp on the accelerator pedal.
I don't know what level of system failure would be necessary for an unintended acceleration event to occur simultaneously to the motor cut-off function also failing, but that's a basic level of prevention that is designed to prevent this from happening. Definitely a step up from a stuck throttle condition in an ICE vehicle