Back on topic here, here's the translation from
Andriasang:
Regarding a possible Kingom Hearts Birth by Sleep download release, Nomura says that this is difficult for a reason he can't say. The problem is separate from Square Enix, Disney or Utada Hikaru (who sings the theme songs). "I want to do something, but it will take time."
I think most everyone would agree that Andriasang is usually right about their Japanese magazine info. So, it's
not the digital rights that are holding it up, it's something else (and whatever it is, it's being worked on).
I'm going to take a wild guess and say that it has something to do with either a) releasing the Final Mix version in the US, b) offering a HD remix for NGP, or c) Birth by Sleep Volume 2.