There are images I use in the Editor as reference, so they should not be exported in the Texture pages. I can place the reference images in a new skeleton if they have no animations, but I also want to preview animations in various contexts and interactions. For example, my character is able to hold different objects or is interacting with animated devices.
Currently, there's no customization when it comes to packing (in 4.0). I would like a way for the Texture Packer to exclude specific folders. Maybe detecting a specific image folder named like "null" and ignoring it during Texture Packing.