This idea came because of this question in the forum and this tutorial video of Lars showing one solution for straight lines.
I would like to see a new joint type (or joint type category) very similar to the pin-Slot, i.e. a constraint on transitional movement, with / without rotational freedom.
But instead of restricting the movement to a plane or axis, restrict it to some more arbitrarily chosen geometry like a sketch-line (which could be a spline) or a surface (which could be bend).
f.e. having a "sphere" joint to such a surface would act like a beetle crawling on that surface, and a sphere joint to a spline curve would only follow the trajectory of that path.
In a sense, "sweep" and "plane along a path" are already performing this type of constraint, but not as a joint.
