A spoon brake on an Ordinary already works too well, resulting in an endo. The same goes for the twin discs on that mostrosity, albeit without the face-destroying descent from 6' up.
You can endo on a Safety of conventional geometry with normal rim brakes, that thing will start tipping at about half the rate of acceleration you can achieve on a normal bike. It might still be twice the rate achievable on an Ordinary, which is why we all ride Safeties now.
A spoon brake on an Ordinary already works too well, resulting in an endo. The same goes for the twin discs on that mostrosity, albeit without the face-destroying descent from 6' up.