Direct driven set-up may not work at the weight we want. In-line motors driving independent but coaxial shafts may need to be sized according to the torque requirements of each prop. If one were to gear the shafts down, then one would have little to no difference over the current contra.
One of the guys from Singapore flew this in Argentina back in 2007, with twin motors driving independant props. It sounded awful as the motors went in and out of phase causing variable beat frequencies
Keith