Thats really neat. Did you make it? Do you have to pedal all the time? I plan to make a future bike featuring a flip flop track hub for a jackshaft and using a flip flop hub with left side pedal drive (1x1) and a 7/8sp freewheel for the right side shifting ability ("jackshaft" to rear wheel cluster). I don't know how much tolerance the track cog will have for the flexi-chain and gear shifting though.