It's not advertised afaik, but this feature kinda already exists. If you type stuff into the comment input, close the tab, and reopen it, you will see "You have autosaved text. Restore". When you click "Restore", you get your text back, so this functions as the sort of draft you are describing, I think.
It's still possible that a more official version of this draft functionality would be worthwhile though.
That's there to prevent losing data if you lose a tab, but it's not quite thereas a draft-comments feature. The part that's missing is the ability to get a list of all the posts/comments you have unfinished replies to. Which seems maybe worth implementing, I'll certainly put it on the wishlist, but I'm not sure it's high-enough priority that we'll get to it.
The part that's missing is the ability to get a list of all the posts/comments you have unfinished replies to.
That feels like a separate feature to me, but it's always tricky say where to draw the lines. The reason I feel this way is because being able to have the draft/autosave for a given post adds value on it's own. If it didn't add value on it's own and the value got "unlocked" by having that list of draft comments, I'd see them both as belonging to a single feature.
My model of most users says that the list of draft comments wouldn't be too valuable. If you only have a few draft comments saved, I'd think that you'd have an easy time remembering what posts you wanted to comment on, in which case you'd just return to that post, click "Restore", and continue where you left off. OTOH, if you had a bunch of posts with draft comments, I could see it getting difficult to keep track of them all, and thus listing them out would be useful. But I don't imagine many people having that long a list.
Edit: As a hack, you could use your browsers bookmarks or LessWrong's bookmarking functionality to keep track of a list of draft comments. Neither is perfect of course.
When thinking about somebody’s post, I often benefit from writing out my thoughts. Usually, I do that in a comment box, because that’s convenient.
Often, I’ll realize that my first thought is wrong, hit on something I want to read before posting, not have time to finish my thought, or feel growing uncertainty about whether it’s worthwhile investing the time to finish my comment. I don’t want to keep track of a bunch of half-formed thoughts on, say, Google Drive. So I delete the comment instead.
It would be nice if I could easily make and save a bunch of hidden comments on the post itself. They’d be essentially “draft comments.”