Hmm… it looks like Square Enix is doing something with the Mana series. Siliconera first found a trademark for Rise of Mana registered in Europe. Square Enix filed a trademark for Rise of Mana for use with video games and computer software in Japan too.
In addition to that, Square Enix re-registered Seiken Densetsu (Holy Sword Legend), the franchise name for the Mana series, earlier this year. Maybe Square Enix is planning on doing something with the Mana series aside from that GREE game.
Drakengard 3 was hinted at through re-registered trademarks. Drag-On Dragoon was registered a couple of months before a new game in the series was revealed.