The Oz website has updated with the new summary for chapter 3 of the photo story! Here it is.
So I guess the "guest appearance" Knightmare that was mentioned before is the Guren Mk-I. (Still no news on which familiar character will be appearing, though.) Since its basically the same as the Guren Mk-II minus the Radiation Wave arm, it will be interesting to see it fight its offshoot, the Byakuen. I'll post a detailed summary for this chapter as soon as I get a hold of scans of it.