With Kingdom Hearts 3D Ultimania now available a few details regarding the future of the Kingdom Hearts franchise have been detailed. As of the moment there are no plans for a Final Mix release of KH3D, there will be an announcement regarding the next title in the near future. Nomura has also stated that he hopes to see a Pixar work in the future of Kingdom Hearts and that multiple titles are currently in production by the Osaka team. Regarding the secret ending of Kingdom Hearts 3D and the possibility of a Birth by Sleep Vol. 2, an excerpt detailed the following.
Does the secret message you unlock mean Kingdom Hearts 3?
Nomura: Use your imagination. You will eventually find the answer.
Volume 2 of Birth by Sleep? Continuation of Birth by Sleep?
Nomura: That is to say the story for BBS vol. 2 exists but that story has been cut off. There is potential for a sequel to Birth by Sleep, but there are no plans for it right now.