MBB is what cruzbikes are.
My concern is the additional motor weight added to the steering mechanism.
Yeah. I wouldn't even try it. Those handlebar baskets on typical town bikes are just barely okay, but such a weight swinging so far away from the steering axis will make steering extremely delayed and the weight will always pull the steering into one direction, because the front falls down, when it is steered.
A motor meant for the rear wheel, that on a Cruzbike sits in the front weheel might be okay for handling but with the limited traction on a front wheel driven bicycle, I'd say that rear wheel (built for normal front wheel) is the only sensible way to go and even would combine the best of all kinds of propulsion.
I think, there ahould even be ones with two-gear-transmissions, if that's what you are worried about. (Only reason for bottom bracket motors, I can see.)