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).
no real place to make such a comment where it's not out-of-place, profile IMHO makes sense then.
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)
I've been surprised at how long it's taken the community to react in this way.