It's kinda a bit too large for most modern anime productions, but I honestly feel like Ar Tonelico II could make for a pretty awesome anime! It's already pretty anime-like, and then you add to that interesting themes and world-building, great plot, amazing music, and tons of messy Mari Okada-style drama. Really, just hire Mari Okada for it and it'd be a ton of fun. (Plus it'd be a good chance to smooth over some of the more dated aspects, and make the Luca/Cloche ending canon.)