Hocopor
We'll probably implement it, but with a slightly different behavior. [rotate:degrees] will behave similarly to the [scale:value] tag.
The image will be exported rotated by degrees, and the corresponding attachment in the JSON will be rotated by -degrees.
This will allow keeping the image visually coherent in Photoshop and Spine, while allowing the actual PNG to be rotated as desired to easily pack it in the atlas.