While this design is kinda cool... Id personally Love to see a Force Feedback Trackball, for use in a Modified Marble Madness Build.
According to Mark Cerney, the developer of Marble Madness... he had intended the Trackballs to have force feedback.
Marks original design was to have four Rollers: Two of the rollers being driven by motors, and Two were the Optical Sensors.
However, it was revealed that you cant get a trackball to move properly, on 4 rollers.
That said...
Why not integrate the Optical Sensor AND the FFB motor, on the same Roller?
(personally, I cant figure out why they didnt think of it.. other than possibly the added costs of machining completely new parts)
Maybe 10yard could add the FFB code, for the game.