Another wacky one which may or may not fit the way people use AR but .... Moho (Anime Studio) has a cool feature where you can import layers from your other layered files. So if I wanted to reuse a sky layer from another AR painting you click import/ select the image and you see a thumbnail of all the layers in that file and can drag one in to your current job.

This also allows you to use some files like 'library' files; you can put several sky layers in one file ie morning sky, night sky, stormy sky etc and then reuse them. It can also become a vehicle for sharing ie "download my sky pack."

As I said, possible wacky idea. Makes sense to me for work if you want to reuse assets.