From Wikipedia:

Kingdom Hearts II and Kingdom Hearts II Final Mix+ have unlockable teasers that show new characters in armor, named Terra, Aqua, and Ven. Tetsuya Nomura has stated that the characters are related to one or more characters already introduced in the Kingdom Hearts series. He has also stated he has ideas for another installment. However, he did not state exactly what he would like to do with a new installment. The Kingdom Hearts team is postponing Kingdom Hearts projects to be able to work on Final Fantasy Versus XIII. In Famitsu, Nomura stated that there are multiple Kingdom Hearts projects in the works, although what those projects consist of is not known. Nomura has referred to the new sequels as a whole new series and stated, "The next title won't just be Kingdom Hearts III. If it were III, we wouldn't call it a new series." He also hinted that this "new series" might involve the character Xehanort. The new game is described as a side story that will focus on other characters. The "new series" is set to be announced at the 2007 Tokyo Game Show.



New series? I don't like the sound of that.