Well those are rumors but Kingdom Hearts 3 is currently not in development. Although there are some truth to what you say. Nomura stated that Kingdom Hearts is not over and there will be a new Kingdom Hearts series revolving more around Xehanort, Mickey, Keyblades, (ect).
The 3 characters in the Secret Endings are important and have meaning to the next series. Nomura wants to explain more about Roxas as well.
This new series is not Kingdom Hearts 3 and this new Kingdom Hearts series is likely to be split up into various installments. But is Sora's journey over? Well look at this:
XIII. Lastly, has Sora's journey come to an end this time? Before you told us "I have the end of Kingdom Hearts in my head", but does this mean that Sora won't be there? There seem to be new developments with the Kingdom Hearts Series, so can you please tell us within the present limits any hints?
Without recalling too much about the mysteries and problems of the outline remaining for KH series thus far, I don't think that Sora's journey is over. If you get to see the ending of KHII I think you will be able to sense some new premonitions. About what I said about the "end" of KH, of course I won't be able to say anything about that yet, but if the numbering of KH were to go to "III", I doubt that Sora would have no relation to it. And even if I wrap up Kingdom Hearts, I don't think that Sora will be irrelevant.
Also, there are many new developments. I think that the news will be able to satisfy the widely supportive KH fans everywhere. Because there is still more to say about this "new" thing, please dare to think with a different flow, rather than just going with what's mainstream. I will give you a hint about the contents of one of the numerous developments. In the freshly added secret movie a phrase comes out, "Fate doesn't happen by accident, there is necessity".
In the near future, when you experience the new Kingdom Hearts, please see about opening this book. I think surely some of these points will tie together. And also at that time, it would be very fortunate if all the fans everywhere have a good time with it. Until an announcement comes, please have your fill of fun with this game and look forward to the next.
That was is in his latest interviews.
Here are my thoughts:
I don't know, maybe people have over looked this, but Nomura says that Sora's journey is not over yet. But as this new series develops, it will connect the past of the Keyblade, Xehanort, and many other things to the current Kingdom Hearts series and that was sort of mentioned by Nomura in some of his interivews.
With that being said, its possible that in the distant future, Sora's primary role as main character may pick up again after everything has been built back up possibly one or even 3 installments from now.
Remeber Kingdom Hearts has everything to do with Sora, although he might not be directly involve with this series, eventually it will all have to connect to Sora being the Keyblade wielder, (ect), and his primary story will have to extend. But like Nomura said, we should take the Kingdom Hearts 2 ending into account, because it has meaning to what we can expect from Sora in the future and possibly the ending of Kingdom Hearts. I think Kingdom Hearts 3 is when Sora's strong will pick up again.
But that is my take on this subject.
-Nomura: The announcement of the new KH project might be announced soon. I think that we can expect the title to be announced in the "hidden-ball play".
Tomo Notes: Hidden-ball play" is a term from baseball in which, a fielder has the ball and hides it from the runner, tricking the runner to think another fielder has the ball or the ball went out of their reach. Once the runner reaches the base, the fielder instantly takes out the ball and outs the runner. In relation to Nomura, he's basically hiding the title behind his back and is waiting to release it to us.
-This "new project" is not Kingdom Hearts 3, rather it is "outside" work. (Meaning, it is more then likely a sidestory?)
-There is still a lot left to tell about Sora's Story, but Nomura wants to draw more towards other characters with this game. This could mean Sora has a lesser role in this game.
-There will be a focus on "Birth By Sleep", as well as Mickey and what was happening while he was in the world of darkness, as well as his keyblade. Nomura also wants to focus on Roxas the most. There are apparently a lot of interesting things left about him.
-This game will be a little different from the Kingdom Hearts Series, with slightly different gameplay as well. As for the system, he is considering portable systems. (Options: PSP, NDS, and Mobile Phones).
So for the first part into this new series, Nomura plans on placing Kingdom Hearts on a portable console. But that does not mean the other installments will be handheld. I think the games require more high tech material will be on the big guy, the big console.