Square Enix is considering bringing its first Final Fantasy MMO -- Final Fantasy XI -- to the PlayStation Vita after it launches later this year.
Hiromichi Tanaka mentioned the possibility to Famitsu, although he has confirmed that no actual plans are yet in place. He added that a PS3 port of the game is definitely not happening, due to difficulties with the hardware. A portable version isn't out of the question, though.
Personally, I'd be quite into that. I'm not a big fan of MMOs on computers and consoles, but their repetitive, grinding nature actually makes them quite appealing on handhelds. I'd be into this.