Material parameters are hard because you have to apply one MID to the whole mesh, which means you need multiple mask textures if you want red gloves and blue trousers. If you have multiple components, you can have one MID per piece, which makes it easier to modify colours etc.
Morph targets are tricky because they map to vertex indices. You would need to add an additional step to duplicate the morph target data when you merge the meshes and remap the verts to the new target mesh. That code doesn’t exist yet.