The ability to have rotatableModelObjects on parts would be nice. This would work great for contra-props, as well as for pulleys and fans on engines, and my axle part.

Oh, yeah, that's from when this had multiple requests in one issue. Not relevant anymore.

Moving parts requires moving hitboxes. Very hard.

We'll need moving hitboxes for all sorts of important things eventually anyways.

Moving hitboxes are different that rotatable parts on parts. The former involves a physical property that's on both the server and client. The latter is simply a visual property that only affects the rendering code.