After more thought I see more of what you're saying. The question of unsaved changes. Sorry I missed that.
What I'm doing is copying the file from disk to a new file. I'd like to be able to make a quick backup *before* I save this file. I could commit to git I know but then recovery /compare etc is more complicated. So I'm not expecting unsaved changes with all the undo etc. I would never ask that of you.
The idea of saving unsaved changes to another file so that I can undo what I have and carry on as if all that never happened. Hm. That would be a wonderful feature to have but I've never had occasion.
Though now that you mention it...