Rondo of Swords hasn’t been announced by Atlus USA, but Nintendo’s Q1/Q2 line up has the Nintendo DS game slated for April. So what is this “mysterious” game? I can’t say this for certain, but I’m betting it is Itsuwari no Rinbukyoku. Success published this last year in Japan and Atlus has a pretty good relationship with them. Also Itsuwari no Rinbukyoku can be translated into Rondo of Deception. It’s not quite Rondo of Swords, but its close and my best guess.
Update: (!) OK this was written last night and Atlus sent over an e-mail confirming Rondo of Swords is Itsuwari no Rinbukyoku. They have an official site up so you can check out the localization is going before you can pick it up in stores on April 15.
Update 2: Got the US trailer too, check it out past the break.