According to Quartermann's reports from 1up, in the latest issue of EGM, speculation is high about a Wii-xclusive spin-off of the Kingdom Hearts franchise. Now, a series of prequels may be in the works for different platforms, much like the Compilation of Final Fantasy VII has done so. The FFVII Compilation has reached PS1, PS2, PSP and mobile phones so far, and the Kingdom Hearts series may very well follow suite.
Kingdom Hearts games have appeared on the Playstation 2 (Kingdom Hearts and Kingdom Hearts II) and the Game Boy Advance (Kingdom Hearts: Chain of Memories.)
Square is expected to make an announcement at this year's Tokyo Game Show, scheduled for late September.