I read a few threads on images and got an idea which seems to me should be very in line with how Drafts work.
What if Drafts add a photo/file picker, which opens Photos/Files, and when a file a picked, it inserts path to that file (with a specific URL scheme for example). Maybe if it’s a photo/image if also adds markdown syntax for inline image, IDK.
This allows for further improvements: showing this image in Preview, and the main one - access to a list of files in a given draft in scripting. There is a FileManager API already, so it seems it’s doable? 
This way I could add file upload to my blog workflow.