Didn't Nate recently make it so you can now pre-strip the whitespace in the source images (externally) and it won't break the meshes/UVs like it used to?
(meaning you don't have to recreate the mesh if the size of the source image changes)
On top of this feature, and in the context of the request, could Spine itself be made so it does that pre-stripping step itself by trimming the source images?
PS
I also haven't seen how this behaves when your intention is to scale (up or down) the resolution of the source image the mesh was mapped to.