Ugh.. it's going to be on BOTH systems.. not just Sony, not just Microsoft.. BOTH! Well, that's the way I saw it in the past thread and the way I still see it. Honestly, if KH3 is not on both systems, I believe it's not going to be living up to its full potential. Going multi-platform to the 360 and PS3 is the best way (imo) for the KH series to live up to its full potential.
Oh, and would Square test the waters of the 360? Honestly, all they'd have to do (should they do the PS3 compilation disk) is port the exact same thing (maybe on two disks instead) over to the 360 and if it prospers, like I feel it would.. voila.. Square will have their reason to put KH3 on both systems.
Seriously though, I'm pretty sure the 360's got a fair portion of the former PS2-owners as well, as the PS3 was severely overpriced up until this Sept. Do you realize how many people probably said "Ahh.. screw it (Sony)" and got either a 360 or a Wii instead? More than likely, the majority of them (of the ones who didn't get a PS3) probably got a 360, seeing how it has a decent library (unlike the Wii, for the most part) and is cheaper than a PS3. (This is ignoring the RROD hype btw.)
Anyways, I believe there is KH fans and lots more potential KH fans to be made on the 360. What's the best way to ensure that you get the most money (out of KH3) as possible? (if you were Square) You "test the waters" with something like the compilation disk(s) (should it be made) and if it works, make KH3 for both systems.