The new Ellsworth The Ride has no sprockets but has a virtually endless gear selection by the use of a da Vinci inspired design for the rear hub. The weight for the system is high right now but I expect that this system will see some off-road implementations in short order.
Removing the derailleurs froma mountain bike would cut down on mechanical issues out on the trail as well as increasing pedaling efficiency. Now if they could do something about the $3k price tag (and the 39 pound bike weight).
