I'd say there's a 70% probability that Persona 5 is a timed exclusive for the 360, that will later be ported to the PS3.
Everything we know about the game follows the exact same pattern as Star Ocean 4 (and to a lesser extent Tales Of Vesperia):
- The developer is hiring 360 developers.
- The developer admits to doing in-house development for the 360 (January 2009 edition of Famitsu 360), but will not confirm any PS3 development. *
- The game is announced in a Playstation friendly magazine, but the platform is kept secret.
Microsoft have announced that there are several unnamed exclusives for the japanese market in development, and Persona 5 is no doubt near the top of Microsoft's wish list. And as a small developer who's been struggling financially in recent years, Atlus can't really afford to say no to a tempting offer from Microsoft.
In the past it's clearly been a deliberate tactic from Microsoft to make sure japanese third party 360 exclusives are announced, but with no mention of the platform (for a while). This way the game will get maximum exposure in the japanese PS3 friendly gaming press. This worked wery well for Star Ocean 4 who was extensively covered by Dengeki Playstation magazine right up to the 360 exclusivity announcement.
PSP exclusivity would kill the popularity of the Persona series in the west, which makes the PSP a highly unlikely choice.
* In a 2008 interview with RPGamer, Aram Jabbari from Atlus USA denies that there is any Shin Megami Tensei title in development for the PS3 ("Sadly, this too is just a rumor").
