Renowned Japanese developer Keiji Inafune, the illustrator and co-designer of Mega Man and producer of Onimusha and Dead Rising has let it slip that he is working on a Vita game.
Speaking at the GDC 2012 panel “The Future of Japanese Games”, Inafune mentioned that he was working on a Vita game. He quickly backtracked, and said that he wasn't supposed to say that, rephrasing his statement to say that he is only working on 3DS and social games. Inafune then told everyone to forget that he had mentioned the Vita.
With Sony Japan planning to reveal a bunch of Vita games on the 9th, it is possible that the game will be revealed then, although, considering we know nothing about the title, the game could have just started development.