In an interview with Famitsu, translated by https://twitter.com/_KH_ENGLISH and posted on Kingdom Hearts Insider, Melody of Memory producer Ichiro Hazama, director Tetsuya Nomura and co-director Masanobu Suzui (director of the Final Fantasy Theatrhythm games) talked about the upcoming rhythm game. When speaking about the KH game's composer, Yoko Shimomura, they had this to say:
What did Shimomura say about this game?
Hazama: Apparently she really enjoys playing the Theatrhythm series, and she has asked us many times over the years if we would make a Kingdom Hearts one. I am sure she is looking forward to this game, and I think we have made something that will satisfy her.
Suzui: Once I met Shimomura at a cherry blossom viewing picnic, and she gave me the full set of Kingdom hearts series CDs. She gave me this "you know what to do now, right?" smile (laughs), so I am sure she's been hoping for us to make a Kingdom Hearts series rhythm game for a long time.