Physbones have a setting to disallow self-collision. However, this setting unilaterally disables collision with both global colliders (hands/fingers, namely), and even manually declared physbone colliders.

This is both restrictive, and also makes no sense. To make a physbone interact with a physbone collider, the physbone component needs to MANUALLY declare the collider it wants to collide with, anyway. If you didn't want physbones to collide with your own physbone colliders, that's the default behavior already if you didn't specifically slot in a collider reference for that physbone component.

If manually-declared physbone colliders ignored the "allow self" checkbox being unticked, creators would be able to differentiate between a physbone's ability to collide with hands, and with physbone colliders.