It always bugged me that the proof went on the profile itself and not on a mere comment like it does for other identities (Twitter → tweet, Reddit → a post in /r/KeybaseProofs etc).
The problem with doing this on HN is that you can’t delete or edit comments after a few hours, so there would be no way to remove the proof besides a reply to your own comment (which also doesn’t work once the thread is old enough to not allow comments)