Imagine the possibilities if there was drag and drop?
Imagined and realized in a multi-purpose multi-choice question type that I developed and used a couple of years ago but has never gotten to release.
A fairly simple solution for modern browsers under the assumption that when you dnd an image into the editor it creates an img tag with the image content in base64. Then it is simply parsing the content of the editor on submission, extracting the base64 image tags from the content, converting to system files (in the user draft area, to be processed with all the other draft files) and replacing in the content with the appropriate pluginfile links.
It worked effectively for my purposes. I don't know how cross-browser/platform such a solution is, but it may be worth examining.