This is semi-old news but I wasn't sure if anyone had heard about it since I failed to find any information on our forums about it. At the Tokyo Games Show last year it was announced that a new Final Fantasy VII: Advent Children will be released under the name Final Fantasy VII: Advance Children Complete (at least for now).
It is not a sequel or anything, just some minor changes and updates and it will be available for Blu-ray. There's also talks of new scenes being added, as well as existing scenes being edited.
Here is a link to the article @ Gamespot:
http://www.gamespot.com/psp/rpg/finalfantasyviiadventchildren