Is EGM's rumor really is true? Looks like it: In a recent interview with Tetsuya Nomura he was quoted saying the following:
"It is not Kingdom Hearts III, but it is an anecdote (extra or side-story) work! I think Sora [still] has a big role to fill! So let's focus on other characters other than Sora for the following work now."
That does confirms EGM's latest rumor saying that the new Kingdom Hearts project is a spin-off. Might be a first for them. The rest of the interview with Nomura is extremely interesting, so make sure to read it if you are a Kingdom Hearts fan.