Square Enix has updated the official Japanese website for Kingdom Hearts HD 1.5 ReMIX with a small little thing… The release date. Kingdom Hearts HD 1.5 ReMIX will be released in Japan on March 14, 2013.
Kingdom Hearts HD 1.5 ReMIX features HD version of Kingdom Hearts 1 Final Mix and Kingdom Hearts Re: Chain of Memories. It will also feature HD cutscenes from Kingdom Hearts 258/2 Days.
You can view the official Japanese website here. There is no word yet on a release in other regions.