Personally, I'd much rather Kingdom Hearts 2.9 be an ultimate collection which contains DDD HD and the past two collections on PS4. There is the idea of something similar to MGS:GZ, but I wouldn't really want that as I'd much rather experience everything in Kingdom Hearts III. Additionally, this isn't possible since the Unreal Engine 4 doesn't run on PS3, which means a KH3 Demo isn't at all possible.
I can just imagine all the past games at 60fps!
I've yet to play DDD yet, so I am really excited either way!
How about you?