The Kingdom Hearts 3D Ultimania guide book is out today, and it has the expected interview with series mastermind Tetsuya Nomura.
A brief summary at FF Reunion reveals that the interview contains a teaser for the next entry (or entries) in the KH series. Nomura says that they've started making a variety of movements for the new title(s) in the series. He believes they'll be able to make an announcement pretty soon.
Osaka team has multiple titles in development. No plans for a Final Mix version of KH3D.
--Does the "Secret Message Unlocked" in KH3D hint at KHIII?
Nomura: About that, I'll leave it to your imagination. Well, you'll get the answer for that later.
Nomura: Maybe in a few years, but no plans for it right now. The Osaka team is really busy. ＼(^o^)／
--Is BbS Volume 2 = BbS2?
Nomura: I used "A Fragmentary Passage" without regard to its context. What I mean is, there's a story for Volume Two, without using that scene. I can't say there isn't a possibility of making it, but there are no plans for it right now.
--The Mysterious KH = 3D?
We interrupted titles in 3D, and we haven't reopened that discussion yet.