If we want realistic mesh deformation even in extreme poses then there would have to be some kind of collision detection of the mesh with itself. Resolving the collision in such a way as to preserve volume while also letting squishy parts squish have solid areas remain solid.
Given my rig is aimed at games then this doesn’t seem feasible. So I end up with the question: at extreme angles, do I want the mesh to loose volume or intersect?
In reality I will have a combination of the two, but my preference is to have the model intersecting. In my experience it’s quite normal to see intersecting character models in games. Having a character who is supposed to be big and imposing (like mine) suddenly loose all their muscle volume however can ruin the atmosphere.
The pictures above show a first pass at skinning the shoulder. as the arm closes there is some deformation of the bicep but mostly the forearm just intersects. In my opinion it looks fairly natural, like the flesh is squidging together.