Re: Real vibration resolution...shaft drive.
I would think that it would be easier to try a toothed-belt drive first.
Also I would expect that most of the vibration comes from the (piston) engine itself, as electric-bicycles tend to use much lower-RPM motors, and those riders rarely ever complain about vibration issues.
(-come to think of it, my hands have gone numb some days while trimming the yard with a weedwacker.... and the weedwacker does use shaft drive.... It also uses a small, high-RPM engine as well-)