The side games were already pretty much non-exclusive. Final Fantasy Tactics is coming to PSP, the next tactics advance is coming to DS. There's also a side-story to Final Fantasy XII coming to DS. Then there's Final Fantasy XI (online) on Xbox 360. Final Fantasy Crystal Chronicles is coming to Wii.
But I am 99% positive that article is a hoax: there have been NO announcements whatsoever on any of the legitimate video game sites, and something like this (the main Final Fantasy series being non-exclusive) would be extremely important to the survival of the PS3.
Okay, it's not a hoax.
http://www.square-haven.com/news/?id=1275
"In fact, the Fabula Nova Crystallis Final Fantasy XIII project isn't just limited to three projects - there are many different aspects. In terms of the formats we're reaching, as well, it's not simply exclusive to the PS3 and mobile phones. In Latin Fabula Nova Crystallis means "New Crystal Story" and we're using that as a basis for the project, but there are many characters and legends that are branching off from the main story and universe. It's a huge project."
So, it seems that there are many games planned for release around the FFXIII world. Squenix definitely seems to have big plans for this iteration of the series, but I would still be willing to bet that the actual "Final Fantasy XIII" and "Final Fantasy XIII Versus" games will remain PS3 exclusive... but even that is kind of iffy, after reading this:
http://www.gamespot.com/news/6167864.html
Sony Computer Entertainment France president Georges Fornay dropped the bombshell in an interview with French-language newspaper Les Dernières Nouvelles d'Alsace (subscription required). He said, "The development costs of games have exploded, and it has become more difficult to have exclusives, outside of our own games. But we have for launch day [in France] 30 games, including MotorStorm, Resistance: Fall of Man, and Virtua Fighter 5. Moreover, we are expecting 200 games [for the PS3] by the end of 2007...As far as Final Fantasy XIII goes, I can tell you that the exclusivity is in discussion."
Sony is definitely going to be kind of screwed if they lose exclusivity on the main Final Fantasy series... I'm really curious to see how this will develop now.