Ah, I thought I'd miss something. Taken that into account, I can understand and agree with where LightAndOblivion is coming from, regarding them reacting to each other. Granted, I think it's important to consider how Vanitas was compared to the likes of Xemnas and Ansem, as if that was him time-traveling rather than being there in the present already.
I'd say I'm more convinced of the idea that he may exist outside of Ven's heart (and fittingly with Xehanort's), but I still wouldn't rule out Ven's heart.
There are so many interviews by now which have some important bits in them that it is easy to overlook one or two. ^__^
Pointing out Vanitas being different compared to Ansem and Xemnas is indeed an important point to keep in mind, but I am not too sure yet in which way because even Ansem and Xemnas are a little murky since Nomura also said regarding them that they may possibly come from a place
entirely outside of time.
We cannot rule out any of these possibilities yet, although I personally hold the one of him being in Ventus' heart as being less probable.
And I don't think Vanitas is time travelling. If he were, then why wouldn't Trollanort just pick him up from when he had a body like Ansem and Xemnas? He could have just picked him up from before the final battle in BBS.
Correct, what further points into this direction is that Nomura explicitly pointed out that Vanitas is "different" from Ansem and Xemnas.
So Vanitas is still around or something?
His essence, aka his heart quite possibly is.
Keep in mind the following two things:
1. Ventus' heart survived the final battle of BBS, albeit badly injured, so it is not
impossible that Vanitas' heart survived as well. Furthermore when one considers that memories are a key ingredient that builds a heart and that those are immortal, as stated already in CoM, it makes even more sense.
2. The golden eyes strongly hint towards Vanitas having a direct connection with Xehanort's heart or even more likely one of his "heart-seeds" inside him, so that would allow his essence to endure due to this connection.