I doubt it will backfire. I expect a skewed version of what we saw with DMC4 and GTA IV (assuming the whole thing stays PS3 only in Japan):
PS3 will sell more WW thanks to Japan and Versus (360 would need to sell a lot more to balance out loss of Japanese sales IMHO)
360 will sell well and may sell more than PS3 in US.
360 will likely gain a modest console spike (I think loyal fans will go with a PS3 if they are making a new console choice but the other 360 jRPGs might swing things a little and drive a modest spike)
PS3 will get a bigger console spike WW, particularly thanks to Japan, where I expect a much bigger spike than we saw for MGS4. This could be helped if Sony get White Knight and other jRPG's out or well marketed before and affter FF release to push notion of playing multiple big jRGPs on the platform.
No one really loses, everyone gains something, and the biggest winner is probably SE as I doubt the current positioning will cause any cannibalization between PS3 / 360 versions but will deliver more sales than an exclusive on either platform.
Try to be reasonable... its easier than you think...
