Motorcycle exhausts are never really an attractive feature of any machine.
Today’s invention is to use the frame of a bike as a conduit for exhaust flow from the engine. This would work particularly well in those machines with large-section box frames (into which various filters might easily be fitted, without significantly increasing ‘back-pressure’ on the engine).
There would be an outlet from the frame, somewhere at the rear of the machine.
This would also lessen the weight of a bike (even if some local strengthening were required and a silencer attached to the exit).