I think 2.9 is a Kingdom Hearts 3 prolouge like Ground Zeroes was to The Phantom Pain. Think of it as an early look at what the game will be like and we will also be introduced to the beginning of the game story wise, maybe even showing Sora obtain his new outfit. If you look back at the beginning of KH2 with the Roxas prolouge, just imagine that being a separate game but most likely more meaty, introducing us to the new gameplay features, such as attraction flow and keyblade transformation.
The fact attraction flow is said to be in it, instantly makes me believe it's a prolouge considering attraction flow is new to the series.
I'd be very happy with a Dream Drop Distance HD but I don't know how it would work on ps3.