The trailer Square Enix released for Piano Opera Final Fantasy I/II/III yesterday confirmed the existence of a Piano Opera Final Fantasy IV/V/VI. Today, Square Enix made formal announcement and opened an official site for the soundtrack.
Piano Opera FinalFantasy IV/V/VI will be released on May 16, priced ¥2,800. It includes music from FFIV, V and VI. Square Enix has not given the track count (I/II/III includes 13 tracks).
Access the official site for some sample songs.