I saw a Rokon a while back. It was the yellow model that seems to be in all the pictures I've seen.
What I remember most about it was the huge sprockets, long chains, and small drive shafts with u-joints to transmit power.
There already is a two wheel drive bike: the Solex!
One long time owner reported that as a kid he got stuck in some mud at the bottom of a long hill. The front tire was spinning with no traction and starting to slide out. Instinctively he pedalled, which helped the bike get free and climb out of there.
He was so excited with his discovery he burned half a tank of fuel repeating his discovery that day.