Ar Tonelico always borderred on the action RPG battle system anyway. I think this'll work very well since you always had button mashing to do while your casters prepped their song magic. My only qualm with the idea is that I hope they still allow how you fight with the melee attackers to affect the properties of the song your casters are singing, and I'm not sure how defending the casters will play a part in the game with this change.
edit: also I really hope they go with an action RPG system that emphasizes damage mitigation in some way. I really dislike action RPG systems where you can just whack away without thinking much about what your enemy is doing.