I hope a potential 2.5 collection would come out before the PS4 is released. Here's what it should have:
Kingdom Hearts II Final Mix+
Kingdom Hearts Birth by Sleep
Kingdom Hearts Re:coded (HD cutscenes)
I do not think Dream Drop Distance will be released on any future PS collections in any form
I hope they do dream drop distance as well, even if it`s not in 2.5 DDD is still the last game in the time line before KH 3, so if not a collection then I hope they do an HD remaster of it and sell it seperatly, there have been HD remastered copies of games before that were not apart of a collection. Although I would perfer it to be included in 2.5, but if it`s like 1.5 they already give us 3 games in on collection. Although I am quite sure DDD will be out on PS3, if not a collection then seperate, one of my reasons for this is because Square Enix has said one of the reasons they are releasing the collections like this is so people can play all the games in the correct time line. That should include DDD.
I also hope 2.5 is out this year although I am fine with next year, just hope it`s not a long wait. I am still waiting for 1.5 to be released this fall in NA, so I hope they are already working on 2.5.