Fascinating, Marty - first thing it made me think of was the turbo-compound arrangements on the Curtiss-Wright R3350 engines which made the Connies so great.
All these tail-end devices waste energy fighting the rotor torque. As a recently energised Kaman fanboi, I rather fancy the Huskie, which uses the exhaust gas usefully: to provide lift. Of course with co-axial rotors, there is no need to fight yaw.