ive been pondering the thing for a while...
problem with hubs for pushies is the drive is on the right, and for a gear shift to work solely on the engine...it would need to be on the left... i havent bothered checking but im assuming these "shift kits" are a jackshaft that then drives the cranks...yuk. the idea just sounds horrible.
on the other hand...if you got a shift kit,and drove the 3 speed hub directly, with a free wheel mounted on the left hand side for pedalling (like some bmx bikes now have the chains on the left!) it would be fairly simple, with only the need for a thread to be machined on the hub to take the left hand freewheel...
then...how do you start? theres a freewheel there! in the 3speed hub!
(ive thought of that too...a recoil spring starter? roll back a bit, then...yeah)
work out how to actually pull one apart and jam its pawls up so it cant freewheel
im gunna do this now...
and do i have the bike?
oh yeah !
but iunno.
ive been told that gear hubs dont take too much torque at all... and ive found a few old ones that have obviously chewed out...shimano suntour, sturmey archers...etc...and not from motors, id say...