I suffer from RSI, and for this I use a 3M ergonomic mouse (highly recommended). I would like to be able to 1) hold a button down 2) move the mouse forward/backwards to emulate using two fingers to scroll a webpage or document up or down.
I was just about to submit a request for this feature.
Pressing modifier keys and moving the mouse for free scrolling within documents and websites (i.e. in all directions like on the trackpad with 2 fingers) would be great and a productivity booster.