Forever, and here is why...
http://www.gamersplatform.com/2008/08/14/the-future-of-kingdom-hearts-360-or-ps3/
What this article pretty much says is why it is very unlikely for KH3 to go multiplat to other systems.Tetsuya(my hero!:D) has invested all of his being into the bettering of PS3's games. He has always been a fan of the Sony line and would like nothing less then to keep his games exclusive to the systems. Tetsuya is testing out the waters of the PS3 with FFVXIII right now, seeing what can possibly work for his brainchild, Kingdom Hearts.
Many will refute this seeing as FFXIII has lost exclusivity of recently. While that may be true, Tetsuya is not the director of FFXIII. FF versus XIII and Kingdom Hearts are his. He can call these kinds of shots because he is seen as a kind of Rockstar in the gaming world. Just like Kojima and David Jaffe. He has created the most successful franchise from Squarenix since Final Fantasy.
Kingdom Hearts III for PS3,exclusive, forever..........
Greatness Awaits
PSN:Forevercloud (looking for Soul Sacrifice Partners!!!)