I like that idea. With a more or less stationary bed that should even allow for true ABL where the bed is leveled to the nozzle. Of course, that needs an expansion board.
I like the idea of multiple motors but they'd have to be synced with a belt to avoid slight discrepancies during homing unless each motor had an endstop.
So, looking at it this way, the board requirements now are:
Dual X, a Y, a Z, three leveling motors and two extruders = 9 stepper ports. That means that a Duex 5 or similar is needed.