Poly-Cylinder/Tube
This shape would be like a disc/ring but 3D, being able to set the n-side count would be cool too for making hexagons and octagons and so on. The ability to cap and uncap like a cone could be useful as well. It'd be good for use cases where you want a 3D ring but the torus just doesn't have the right silhouette. Or stuff like this:
A. a cylinder/tube primitive with en cap removal
B. variable detail level on 3D primitives
I'll consider this topic to be about A rather than B! B requires a lot of design (and code) work if we want to keep things instanced and optimized. I've opened a separate topic on this: https://shapes.userecho.com/communities/1/topics/11-custom-polycountdetail-level-for-3d-primitives
currently, as a workaround, cylinders can be made by using 3D lines with end caps set to none (which is why I never made a cylinder primitive to begin with)