Not a mechanical engineer. This design is interesting. Do you think regulation is the only reason this did not happen yet? Why is nobody building this otherwise?
* Regulation. Plenty of countries are very specific about the exact mechanicals of brakes, in laws that are 100+ years old from when runaway cars killed people.
* Unsprung mass. Cars handle better if the wheels are very light and all heavy bits are in the body of the car.
* Large diameter motors are harder to design - there is no opportunity for a gearbox, so you lose one design parameter, and need the motor magnetics to be right around the rim of the wheel to make up for it.
* Difficulty of making the air gap within the motor very thin at such large diameters - you end up needing super large diameter roller bearings.
However, I think despite those downsides, the benefits outweigh them.
1. Braking generates a LOT of energy which needs to be sent somewhere very quickly. Each wheel might need to dissipate hundreds of kW of power, simultaneously, on-demand, at any time in normal situations where mechanical brakes function fine today. This is not inexpensive.
2. Today, most EVs do not have 1 motor per wheel, which would be almost surely required to implement this type of system effectively. That's also not inexpensive and unless you can actually put the motor in the wheel-area you still need an axle to connect the motor to the wheel due to the suspension and steering movement, and then that axle would need to be able to sustain these braking forces.
It surely could be done from an engineering point of view today, it's just going to add tremendous cost over using conventional mechanical brakes regardless of if those brakes are a traditional hydraulic type or if they're a brake by wire system.
Not sure I'm convinced by the torque claim -- we've seen cars skidding / losing traction in both scenarios (accelerating and braking). ABS brakes were developed specifically to prevent that (and so was Traction Control).
My experience with electric vehicles is limited to a Boosted longboard, so take this with a grain of sand -- but it seems to me that electric motors are as effective at braking as they are at accelerating.
Putting a motor on each wheel could have some performance benefits, but I'm not sure I'd pay for it if I could get a single-motor car for cheaper. I'm talking about "econo box" performance, which is all I want anyway.