This test makes me confident that the hierarchical motion mapping idea is worth pursing:
This is a very simple mapping of the upper body motion of Tofail Ahmed as he sings an khyal alaap in raag Bhairavi.
The spheres follow the middle finger and thumb endpoints, with the camera in the viewer position facing Tofail.
The planks are linked in a parenting hierarchy and receive local rotations of bones in the skeleton. (The capacity to do this is easily missed in Blender: when identifying the target object of a Copy Rotations constraint, one indicate the armature, then a second drop down will appear that lets one indicate the target bone.)
Also, to smooth out issues I was having with sudden shifts in the thorax and pelvis rotations, I substituted in the head at the thorax point and made that the root. So the line is head : clavicle: humerus : radius : <hand : finger > <thumb>.
An empty provides parenting to the root, and the empty is rotated 180° on each axis across the whole performance. This provides a foundation of slow, continuous motion to match, if you will, the fundamental drone. The head block, then, applies the rotations from the head as an offset to this base angle.
I'm intrigued by the juxtaposition of the direct position mapping (the balls) with the hierarchical mapping (the planks).