I believe GM is using some sort of rust resistant coating on the Volt's rotors. Why cant they use stainless steel (perhaps a special alloy that is somewhat rust resistant and can handle heat) or aluminum for the rotors?
Nissan can blend in as much regen to the friction brakes as they want, and still retain a mechanical failsafe and good brake pedal feel.. you step on the pedal, the piston in the master cylinder moves but the hydraulic pressure is shunted off with a failsafe electronic valve while the big drive motor takes care of the regen braking. A small motor pushes back on the brake pedal to fool you
I dont know how Nissan does it but that sounds like the logical simple way to do it. Mechanical failsafe braking must be retained no matter what.