Obviously, the XF developer team would need to create a better implementation than what I just pictured. From my experience as a forum admin, having the ability to add comments to posts is often the best way to inform members that they've made a minor mistake. It's much quicker than sending them a PM because it can be added directly from the edit post page, but is not as harsh as an official warning. I know that not all forum admins will use this, but for me it would be a major selling point. And if not added to the official release, I'm sure that a modification will be released for this eventually.
Any thoughts or opinions? (Both negative and positive.)