Last I checked, the Japanese wiki didn't have anything beyond 6-4. So few people have cleared it that they're probably in no rush to add content that hardly anyone will have access to.
That's kinda disappointing, but I do see your point. Only three people have killed nami, and 2 including myself masamune on server 2. I was just hoping that it would be soon, so I would have a reason to continue trying to upgrade, other than pvp.