KHII.8's intro seems to suggest that Venitas and Terranort will be Seekers.
Vanitas and Terra-Xehanort I can see, but Ventus-Vanitas?
That's just Vanitas possessing Ventus' body, a "being" that arguably existed not long enough to be grabbed as a seeker and is practically only Vanitas with a different haistyle and color.
Also, some of you seem to have the whole thing backwards as the Wayfinders going dark and "swirling" around the Org throne room happens
before the scene with Aqua facing Ventus-Vanitas and Terranort.
This serves as a callback/reminder to Aqua's two final bosses in actual BBS, Ventus-Vanitas wielding the proto-X-blade being a further hint towards it.
I'd assume that the darkened Wayfinders swirling around the throne room coming before it serve as a visual connection of the events of BBS with Xehanort's overall intentions in general (the thirteen seeker-plot, symbolized by the throne room, was always in the background as a back-up plan), but not decisively as an outlook to the actual future.
It seems that 0.2 will be somewhat an acid trip down the memory lane for Aqua with lots of self-blame/loathing on her part for "failing" to save Terra and Ven from the grasp of Xehanort, concerning the former she not knowing if he regained control or not and concerning the latter knowing that "ending" the enemy's forced control of him resulted in his heart being smashed/lost (I imagine the Ven-in-a-box...err coffin-scene also being related to that).
Phantom versions of Ventus-Vanitas and Terra-Xehanort could even be bosses for her somewhere down the line, possibly helping her overcome the self-blame and doubt eventually (possibly with Mickey's help) and with her new-found faith it may actually lead to the scene with Terra's and Ven's keyblades trashing some Darksides.