do you see a trend? as you add more primitives the number of pairwise checks you have to code starts to get ridiculous. now you could always use the 'tapered' version for normal cyliders and capsules, but that is not necessarily going to be efficient.
just because you can add a feature, does not mean you should.. cylinders are hard enough as it is, who the hell has a perfect tapered_cylinder and who even cares? what is a 'tapered_cylinder' even good for?