Kingdom Hearts HD The Final Chapter 2.8 Prologue is the complete KH saga to date. It includes the newly remastered Kingdom Hearts Dream Drop Distance, Kingdom Hearts Unchained X, and a new chapter that takes place after the events of Kingdom Hearts Birth by Sleep. It is going to be released sometime in 2016, the new chapter seems like it is going to include a lost page in the Kingdom Hearts saga and possibly the reveal of a traitor!
At the end of the trailer there is also footage of new gameplay for Kingdom Hearts III.
To see the first Kingdom Hearts III trailer go to Kingdom Hearts III Big Hero 6 Announcement.