Well my point is you can make that backup now for any books you already purchased and if they change it in the future you can decide to not buy any more books.

Well my point is you can make that backup now for any books you already purchased and if they change it in the future you can decide to not buy any more books. Spotify doesn't let you buy any music so I have never wanted to strip its DRM and haven't even looked into how to do it.