What i'm currently working on, just to be different is what I call a double single speed.
Basically 2 front chain rings and 2 rear cogs. Reverse pull rear derailuer, normal front so they pull the same way. I then have 1 thumb shifter with the cable running underneith the down tube, which then using a canti stradle thing I have split the cable to the front and rear derailuer together.
When I move the shifter it shifts both derailuers at the same time shifting it from 1 ratio to another. Just working on the spacings of the rings and cogs.
Cause as far as i know it hasn't been done before.
you must be like me ,in that you love fannying about with things
you tried dual braking yet ?,both brakes from 1 lever , its suprisingly effective ,but i did find i liked individual brake control better in real techhy
trails , but super cool on a cruiser