I have a 1983 Honda VT500 that I will be aeromoding to see what can be achieved. The challenge is not being able to change the final drive. I suspect that getting into the 70mpg range should be fairly straight forward the real challenge will be getting into the 80mpg range at 70 mph on the interstate, or under the Vetter Challenge conditions. Low&Slow has already started on his Yamaha 550cc Verago V-twin.
I suspect there are others out their with shaft drive motorcycle who could take up the challenge. The nice thing about the VT500 is that in 6th gear on the highway the slitest hill or head wind forces you to shift down a gear. At present the engine turns 5000rpm at 120km/hr [75mph], the improved aero would make highway cruising in 6th gear that much better.