Vanilla has had a great CMS for some time
If you take a look at this page:
you will see what is really a great CMS idea for a forum. Content item has comments that are linked to the forum. Forum discussion feed includes labels identifying that the discussions are related to a content item, and links back to that content item. Now just expand this idea a little bit to other usual CMS stuff like a gallery and you have a pretty kick-ass CMS with a great forum, and a centralized comment feed system in the "all discussions" forum view. Almost a perfect CMS for certain applications.
Alas if only it was a plugin or application....