It would be cool to have a joint which is a slider, but can follow a selected curved line path.
To set it, one would select a line instead of a point, and then the joint origin would snap to the center of the guide line's length. Outer travel limits would be defined by the line's start and end points respectively, then the dialog would allow setting additional + and - travel limits within this range.
If the selected line is a closed loop or circle, etc, then provide a checkbox for unlimited circular travel, and/or start/stop distances or "phase angle" like a model train set, for example. Phase angle would be calculated by the length of the travel distance = 360 degrees; half the travel distance would be 180 degrees, etc. Or, you could use percentage of length as path waypoint references as well. I am sure someone already did this in other software, so look up examples to see how this kind of animal is mapped out to nice dialog box options.