Awesome, if you're looking for another language that "tries to formalize X", where X='3D Rigid object', look up OpenSCAD. You build complex shapes using primitives (using a descriptive language), but the idea is a bit different.

I like the mockup aspect of this: trying to capture functionality and abstracting away detailed looks or positions. I'm thinking of a system where mechanical ideas can be tried quickly to get a functional idea of whether they work, using a maximally abstract functionally-equivalent basis of elements.

I feel like common mechanical subsystems like cams (which, for example, allow a rod to follow an arbitrary velocity curve when you move a knob), gears, and other devices may be abstracted away by a simple primitive (plus something like a descriptive curve or function). Your system of 'wagons' and 'tracks' seems to achieve this, at least partially. It's like when, in programming, we use a high level, abstract description of behavior. Perhaps it would be possible to analogously "compile" wagons, tracks and probes into actual mechanical elements like gears, cams, rods and shafts.

Abstraction is a powerful tool! (for creativity, productivity, expressiveness, and fun)