Recently, Atlus registered a teaser site only showing the site's web address. However there is something familiar about this site, it is in the style of Persona 4.
The black text and yellow background kind of hints that whatever Atlus is planning, must revolve around Shin Megami Tensei: Persona 4. I personally believe that Altus is going to re-release Persona 4 on the Sony PSP. It makes sense because Persona, Persona 2: Innocent Sin, and Persona 3 have all been ported to the PSP in the last few years. I also feel that Atlus is doing this now because in a few months, the anime adaptation of Persona 4 will air and they can bank on that momentum to make this a bestseller.
Now, one can also speculate that Atlus could re-release Persona 4 on the Playstation 3 and/or Xbox 360. I could see that they can market it as an HD version with Improved graphics and possibly more content.
To be honest, I'll be happy with whatever Atlus does with that property because I know that anything they make, will be great. So, what are you speculating that Atlus is hinting at?