This thread reminds me of my buddy Henry's attempt to build a two-wheel drive bike, similar to a Rokon. His idea was to include two-wheel steering, so as to make it more maneuverable in tight quarters; sort of a two-wheel "rock-crawler". After spending a small fortune on universal joints, sprockets, chains, and pillow-block bearings, the thing was a total failure, developing a death wobble at any speed over 5 MPH.
He didn't build it because anyone paid him, he built it for the challenge and fun of it, and he knew when it was time to move on to other projects, like the XR 500 powered minibike burn-out machine.