If the issue here is that you want to send all of the diff comments in a single email, why not just send those on a timed basis? E.g.: I have submitted a diff, and someone comes to review it. If there's a new comment within 5 minutes (maybe less or more, not sure about the exact time), it doesn't get mailed. If we don't have any new comments for these 5 minutes, all new comments get collected into a single email. No need for comment drafts at all, only maybe you'd have to add a timer under every draft saying that it will get saved in 5 mins, no need to click the Submit button under an empty textarea.