I personally see P5 going to a portable myself. Those are the cheapest to develop for with the largest bases of RPG fans. The DS is seeing the new SMT games, and the PSP is getting the Persona remakes, so I'd lean a bit more toward the PSP. For those thinking that the PSP means low sales outside Japan, remember that most of Atlus' games aren't huge sellers. And, they sell to their dedicated fanbase. A majority of the people who bought P1 in the US will probably by P3P, and would buy P5 PSP. Conversely, a good chunk of those who bought Strange Journey would buy a P5 DS.
So what about the PS3? I don't think so. The SMT project announced for the PS3 at launch? It's probably cancelled. There was speculation that it was Persona 4, which is possible. However, in either case, remember that in Japan, Persona is NOT marketed as a SMT game. So announcing an SMT game does not mean a Persona game to Japan.
But Atlus was hiring PS3/360 people! That doesn't mean that they're going to jump into the frey with their biggest series right off the bat! I'd guess that they'd be starting with some PSN/XBL games to get used to the architecture. And games like 3D-Dot Game Heroes or Demons' Souls? Those were solely localized by Atlus USA; recall that it is Atlus Japan who makes the Persona series.
I still see other problems, too. Atlus is first and foremost, a Japanese company. I still think that the PS3 installbase there is too low with too high of a development cost to make the game exclusive. And the 360 is basically dead in Japan. Atlus would not be able to recoup their costs of an HD Persona on the installbase in Japan. As for the Wii, while it is cheaper with a larger install base, and they have experience in developing on it, so it's has a possibility. But, Atlus Japan is not doing too well financially. They want more of a sure thing. And I really think that the portables are Atlus' best shot.