I think this is an excellent idea !
If you purchased a separate motor controller and battery charger the cost is double of what a combined dual mode controller would be. That cost savings would offset the continuous duty cycle of the dual mode controller. Adding a separate Charger PCB to the modular ReVolt (Controller PCB, Power PCB) would be great !
For safety, the dual mode controller firmware would disable the motor main contactors during charging mode. If you added BMS you would have everything in one package, just add batteries !!!
-Mark