The systems itself doing ABS isn't that hard, other than the tone rings and the wheel speed sensors in the wheels.

The thing about it is you need to know a lot about your vehicle, especially if you're looking for a yaw-rate sensor, or any type of ESC. Then there's calibrating it. Probably not too hard to do for a big race team. The OE's spend at least a few months calibrating factory ABS (and years when you think about all the other features in modern cars)

Sounds like in the Bosch unit mentioned they are doing BTCS (Brake traction) and EBD (electronic brake force distribution). This can really help the balance on your car and therefore improve lap times.

You won't be able to use a modern one from a Charger or whatever because of the in-vehicle bus communication. Otherwise the hardware would be pretty adaptable.