We might get a plugin/feature for this in 4.1.
What he means Daniel is they have an article, then the comments as usual. But the same article it's comments are also replicated in the Kunena forum as a thread and posts. Without duplicating the database data - taking it from one common location (either Kunena table or JoomlaComment table).
It can be useful for commercial purposes. Say it's a webdesign or software design community. The comments will be shown, except e.g. code boxes and quotes, and everything past 200 characters. The forums however would be member-only where the premium/club members can reply and also see complete threads.
I imagine this would be a good premium plugin idea.