Reason for the feature
This would make uploading successive alternate versions of images from multi-image social media posts easier then having to copy and paste the same url every time

How it would work
It would be listed as a checkmark beneath the "No available source". When checked, it would read the user's previous upload source url(s) and directly copy it into the source bar(s)

I agree that would be pretty useful.

Hm never tested if it's possible to post "source:url" in the tags when posting like you can add "parent:number".