You can take a look at that nodebb-plugin-imgbed one, that's a pretty good example of saving settings too...
/shameless plug
I was thinking of making this plugin if nobody's already done so. Would just need to observe filter:post.save and purge to remove the history entries. It'd be nice to store just the diffs to save space, if there's already a library to handle diff->json and json back to applying a diff.
One concern I'd have is being able to display an edit history gui for a post that is theme agnostic. Not sure there's a way to do that? A modal with custom styling might be the best option in that case.