I mean, it makes sence. In the 'Trailer' it shows parts of all the games and with the 'Reconnect' thing (I cant remember what game it was in) it could mean that Vol.2 fills all the plot wholes we dont know about in the story.
Like, is Ven still at castle oblivion? How/Why did Riku accept the darkness, his side of the story in KH 1. those are a few things but by far the most important one is Terra-Xehanort/Xehanort. Im assuming KHIII is going to feature Master Xehanort and his other forms in the game hence the reason why sora is going to save aqua and ven for the 2nd keyblade war with Xehanort and Org 13 or whatever, etc.
But it would be cool if the game kind of linked everything together and act as sort of a side story for KH 3.
Everything i said probably dosnt make sense and is probably a load of crap ive made up because i've kind of forgotten half of the up to date stuff and i haven't played KH 3D only watched the cutscences lol
KH 3 will probably be a next gen PlayStation launch title and BBS 2 (If it happens) will probably be a PS Vita exclusive, considering its the successor to the psp so it makes sense and its the only portable without a KH game atm lol
EDIT: Okay so i read it was cancelled? Or at least theres no plans for it, but that dosnt mean it will never happen