[elhigh]

It sounds awfully complex. And I worry that adding yet another step into the drivetrain is just one more little drain on what is a very small resource. When all you've got is humanpower for motive effort, I say the most direct transfer of power is the best option.

Have you read about the NuVinci CVT? I don't remember what the efficiency numbers are but they're pretty good, and it's small enough to be a relatively unobtrusive in-hub installation.