The only place I can see myself posting content about Sigmascape Savage and/or Ultimate fights is in General Discussion, and it doesn't make sense to post specific fight mechanics or high-end strategies in that section.

Instead, what I recommend is a new section in the Gameplay forum (alongside Dungeons, FATEs, etc.) for discussion of Extreme trials, Savage raids, and Ultimate fights and all content of such nature.

As an aside, another section for Eureka is great as well as there are a fair number of people invested in that type of discussion (how Notorious Monster mechanics work, forming parties for Eureka, etc.) too.