Kingdom Hearts director Nomura talked about this upcoming collection releasing this December Worldwide in great detail this E3. Below is everything he covered about each game in the collection plus some information concerning other projects he is working on/was asked about.
Source: NeoGaf VIA Nova Crystals

Kingdom Hearts: Birth by Sleep 0.2 -A Fragmentary Passage-

• Nomura discussed how they can easily alter the game thanks to Unreal Engine 4, especially in regards to lighting.
• What’s in the E3 2016 show floor demo will be in the final version of the game. He wanted to give players something to explore, somewhere they’d have to get high up to get a feel for the area before proceeding. Nomura says Kingdom Hearts III will have a similar feel to it, where free-running to  high places and figuring out the map will be necessary.
• Nomura says that time has stopped in this place only, and that moving to different locations will result in different “effects.”
• Regarding the battle system, Nomura says that the concept of Command Styles from Birth by Sleep has been transferred to Keyblade Transformations in Kingdom Hearts III.
• Nomura calls the Heartless Swarm a “Devil’s Wave,” and mentions that they’ve been present since the first Kingdom Hearts III trailer at E3 2013, and that they’re still not at full power.
• Aqua will only gain strength through leveling up. There are no new Keyblades for her to obtain.
• When discussing the length of Kingdom Hearts: Birth by Sleep 0.2 -A Fragmentary Passage-, Nomura states that it will feature a lot of cutscenes.
• The intended play order, according to Nomura, is Dream Drop Distance, then -A Fragmentary Passage-,then Kingdom Hearts III.
• Kingdom Hearts Birth by Sleep 0.2 -A Fragmentary Passage- is not entirely scrapped content fromKingdom Hearts III. It was something Nomura felt the need to make, but he didn’t want to slow down the pace of storytelling in Kingdom Hearts III with a lot of backstory, so he cut it out and created a separate installment based upon it.
• Kingdom Hearts III will have a short prelude before the game fully begins to make sure everyone is caught up with the story.

Kingdom Hearts: Dream Drop Distance HD

• Nomura discussed the Catanuki, explaining that it was something the Osaka team really wanted to add to the game. He also discusses the addition of PlayStation 4 Trophies, the game now running at 60 frames per second, and the difficulties in transitioning Kingdom Hearts: Dream Drop Distance into to a game without two screens to work with. He also mentioned the “spirit” of developing for the unique elements of the 3DS continues in now developing for the unique elements of PlayStation 4.

Kingdom Hearts χ: Back Cover

• Kingdom Hearts χ: Back Cover is being developed with the same tech as Kingdom Hearts III.
• Famitsu asked if the Black Coat is the Foreteller’s Master. According to Nomura, it is. He is a “unique glue” between them, and apparently has nicknames for each of the Foretellers.
• Kingdom Hearts: Unchained χ recently hit four million downloads in North America, and after release there was an increasing demand to release it in Europe. He is very happy for this chapter of Kingdom Hearts to be brought to fans around the world.
• Nomura hints that the Kingdom Hearts: Unchained χ story will soon branch from the Kingdom Hearts χ story. Kingdom Hearts χ is complete, but Kingdom Hearts: Unchained χ can be considered a second part.
• Nomura indicates that Kingdom Hearts III may hit Japan slightly earlier than the rest of the world, but it will be nearly simultaneous in when it releases.
• Kingdom Hearts HD 2.8: Final Chapter Prologue is in the final stages of production, with English recording currently being mastered and timed. He also told fans to please be patient and wait until this winter for new Kingdom Hearts III information to be released, and to focus on Kingdom Hearts HD 2.8: Final Chapter Prologue in the mean time.
• Next year is the 15th anniversary of Kingdom Hearts, and also the 30th anniversary of Final Fantasy; he told fans to anticipate a lot of features next year relating to those series, and that he wants to liven things up, starting with Kingdom Hearts HD 2.8 Final Chapter Prologue.

Final Fantasy VII Remake

• Nomura states that the game is still a while away, but not to worry and that production is going at a steady pace. He also states that concrete information on the game will be released at a later time and that when it is next shown, he will appear publicly to reveal it.

On a Potential The World Ends With You Sequel

• Nomura said that when it comes to The World Ends With You, its following is very big overseas. He goes on to state that many people, especially overseas request that a sequel be made. Nomura adds that this is no easy task, but the possibility of a new entry isn’t completely ruled out. He wants to ensure that he will have the staff and team needed to deliver an product equal to the original game.