Okay so crazy idea what if Vanitas is going to be one of the vessels for the thirteen hearts of darkness now here is why I say this in KH 2.8's trailer we see the Ventus/Vanitas go in to one of the seats plus every one has wondered why we saw Vanitas behind young Xehanort but he could already be a part of them and he was just in hinding reforming this could explain the lingering spirt of Vanitas and this is either a back up plan made by Xehanort or Vanitas now this is just a theory but I believe Vanitas will come back very soon so please support or critize to your hearts content

Considering he was already a Xehanort vessel in Birth By Sleep, as seen with his yellow eyes, he's an obvious candidate to be a member of the Seekers of Darkness. We can even see his keychain in the chess pieces of the KH3 E3 2015 trailer.

He's definitely going to be a seeker of darkness. All signs point to it.

Vanitas (or Ventus-Vanitas) is definitely one of the Seekers of Darkness, but we don't know who the 13th vessel is when it's supposed to be Sora.

Yes yes yes! I firmly believe he could very well be the thirteenth darkness! I mean, I am sure we haven't seen the last of him and Time Travel would make that possible.