You would then get a locomotive with eight wheel drive, yes, it would mean some additional re-design but I wouldn't think it was insurmountable to do.
Not insurmountable but additional expense. The truck being considered for the new GP7 is probably a reuse of the current Baldwin truck which was changed to vertical drive a few models ago. Reuse of existing parts is a money saver. I too wouldn't mind a dual motor GP but I understand the price point considerations. The vertical motors are much better pullers than the horizontal cans were.