Something else I've been thinking about...

A motor of a given Kv will turn at X RPM for Y voltage across its terminals. The same motor would generate approximately Y voltage across its terminals if its stator is turned at X RPM by an outside force.

A battery will only draw current and store charge if a voltage potential greater than its own is connected across its terminals. Regenerative braking from a drive motor would require one or more of the following to recharge the battery under braking:

1. Accelerating the vehicle beyond the top speed at which the motor's RPM would be at its no load RPM given its Kv rating and pack voltage. ie. drive down a very very steep hill, maybe.

2. Have the ESC step up the output voltage of the motor under braking.

3. A drive system that mechanically regears the motor under a braking condition so that it spins faster.

I don't know how full scale regen braking works to recharge the battery, but I would guess (2) is the most practical...