If you brake too hard on a bicycle, you flip over too, especially downhill. You can brake up until the point that you've popped a front wheelie. Bicyclists usually forgo most of the available braking force, by solely using the rear brake, for this reason. Same for monocycles. If you go past 90 degrees, there's no point in further braking force. If the brakes are electric, they would throttle themselves to that limit, so you have max braking force. Just like anti-lock brakes on a car.
All that said, the terrible wheel-to-rider leverage ratio dooms the design to always have poor stopping distance. Probably not any worse that a bicycle without a front brake, though.
All that said, the terrible wheel-to-rider leverage ratio dooms the design to always have poor stopping distance. Probably not any worse that a bicycle without a front brake, though.