KH will go where the money goes; simple as that.
I think that would depend on what game they are making. If it is KH3, it will definitely be on a Sony title, whether it goes multiplatform to Microsoft or Nintendo I can't say, but even if all the next gens were out and the PS4 was selling badly, I'm sure they would still end up putting it on PS4. If it isn't numbered in the title, then I would say it is free game as to whether it is Sony or Microsoft. However, I can't see a KH game ever being an Xbox-exclusive, even if all the money went there.