Regen exiszts on the XB-600
The DrainBrain is a delight.
one of the first things I investigated was the electical braking. While is clearly is electrical (non-existent when the ignition is off), the amount of charge put back in the battery is minimal; most of the motor's generated power is just sent back to the motor, known in other applications as "dynamic braking."
However, when coasting above 22 MPH, the DrainBrain shows ~350 watts of power being returned to the battery. I don't know whether this is an example of designed regen or merely back-EMF "overflowing into the battery.