I have a suggestion that I've been thinking about for a while. If the desire takes me I might try to add a simple version of it myself.
The collision skin object has addition but is lacking subtraction. The concept of boolean operations is simple, but the execution is complicated. I refined my idea a little to a set of pre-defined procedural shapes with specific parameters.
An example would be a hollow tube, defined by its radius, height and inner radius. Although it's possible to do this with a mesh, it would be far more efficient to broaden the collision test to say "If I'm in cylinder A I'm colliding with it, but if I'm also in cylinder B I'm only colliding with the interior of B."
I put a screenshot of the kind of procedural combination primitives you could make. By far the most useful is the tube, but the sliced tube and cylinder/box combination would also be very useful.
I'd also be keen on seeing subsections of existing primitives such as a cylinder that only lathes by a defined amount, potentially giving you a filled halfpipe.
The benefit of course is that these shapes would be much faster to process than static meshes and would simplify constructing collision skins with primitives.