I've always wanted to create a two point tied chain with physbones for stuff like gun slings, jean chains and such.

I think an addition to the multi-child behavior to allow physbone effects to back propagate up toward the root (Reverse)

and also a Bi-directional effect where the root and child bones effect toward the middle (or perhaps the physbone force is negated backwards), creating a sort of a normal distribution, would allow for physbones to seem like they have multiple points attached.

It would still be limited to one physbone, so maybe a more advanced system would be to be able to attach two seperate physbones at their endpoints allowing for avatars to have a rope in one hand connecting to the other hand, sagging in the middle.