Very neat tool, good job!
There's a fair amount of setup, I wonder how much could be automated.
Mapping 3D to 2D is difficult for perspective changes. I guess that is why you didn't map the shoulders? When some bones aren't mapped, it can lose some of the important details. I wonder if you mapped all the bones if you could find ways to make the perspective changes look OK. For example, using this cube perspective setup for the shoulders: