Maybe an alternative would be to have a json file next to the image file that contains the image attributes. It would be simple to set width/height using a simple script and would be quick to load on build. Such a file could also be useful for setting alt text for an image (alt text should be context independent). For a image file named kitty.png, load the optional file kitty.png.json which may contain the keys alt, height, width,loading. I don't see how align or scale would be useful.
scale option in docutils.conf