I've had screenshots from back there since the 1/8/2015. I'm wondering what that will be in the future. The emblem on the banners on the back wall if no one has noticed are also on the banners in the arena for Valus Ta'arc. I think this area will be used for a sub-unit related to the Valus. Maybe it'll be the Ice Reapers or Dust Giants branch. Unrelated note, in the Grottos on Earth, there is a bunker door similar to seraphim vault that leads to a dark, unfinished cave if you want to check that out as well.