Not meant to flame: why do people want these? They always just seemed like spam cluttering up an article's comments, removing the space for actual discussion.
I would love to see mentions implemented in the UX as a completely separate concept from comments, where there is independently maybe a "mentioned x times" in the post footer which can be clicked for a list of mentioners. This could be a cool method for "webring-style" discovery of websites on similar topics without cluttering up the comment experience.