Now I have no idea as to how international law works and if NISA has the localization rights locked up for all games in the series already, but it seems to me that Ar Tonelico 3 would be the perfect type of game for Aksys to look into bringing stateside. The series already has a strong following in the west and features the same stylish anime art, solid storylines, great character development, and quirky Japanese appeal which is typical of all of Aksys' releases. Additionally the music is always far and above that found in your typical jrpg and even rivals (and surpasses in many instances) those found in multi-million dollar budget behemoths like Final Fantasy. It seems to me that Ar Tonelico would be a relatively low risk/high reward proposition in comparison to some of the titles Aksys has localized so far.
After seeing the absolutely fantastic translation jobs Aksys has done with Guilty Gear, Blazblue and Agarest War (and after the debacle which was Ar Tonelico 2's localization), I would much prefer a company like Aksys to be handling the game versus NISA.