Tetsuya Nomura has recently given an interview regarding the newest Kingdom Hearts collection; more specifically he went into detail about Kingdom Hearts 0.2 Birth by Sleep -A Fragmentary Passage-.
According to Nomura, Kingdom Hearts 0.2 was created as a way for fans to get a taste of Kingdom Hearts III sooner rather than later as 0.2 is created using Kingdom Heart III's technology. The episode follows Aqua and begins immediately after the events of the secret episode in Kingdom Hearts: Birth by Sleep Final Mix with the episode's content being equal to that of a what you would expect from a single world in the Kingdom Hearts series.
Nomura also provided insight to the other two titles included in the collection as well; stating that Kingdom Hearts 3D is essentially a complete remake as the game is making the jump from a gaming platform with two screens to one that uses a single screen. Nomura has also stated that Kingdom Hearts χ Back Cover will be utilizing some of Kingdom Hearts III's technology as well.
News via SiliconEra and Gematsu
Nomura Interview About Kingdom Hearts 2.8