If anything I think you potentially have the progression of development backwards.
I'm quite willing to bet there has been a very clear plot line for the KH1-3 story as far back as when 2 began development. You don't write a trilogy story's middle without at least some idea of where you're going/what you're doing in the end. However SE, even at that time already beginning to see their old flagships' stability (Final Fantasy and the ever widening division each post VII title has been creating, Star Ocean and the disaster that is every game post II, ect.) crumbling away, immediately recognized the 'cash cow' potential of this franchise from day one.
Multiple ties ins, merchandising, there was no way they would allow the original creators to just 'get away' with a 1, 2, 3 operation. Everything outside of the main numbered stories has pretty much had 'executive meddling' written all over it. It's not that they, the creators, don't know what to do with KH. It's that they're not being allowed to do what they want.
Personally I think even the jingle of that one extra yen isn't even enough anymore for SE to ignore the creaking of KH's support strains giving way under the massive slough of side-content they've been piling on. I would say these re-releases are a build up to KH3's inevitable release. They're going to make a huge deal out of it, utilize these re-dos as a form of 'count down' and make a massive parade out of it, turn KH 3 into the 'new FF VII' in terms of fiscal and public receptions. (As SE has pretty much publicly admitted they use VII as the base line for 'How well are we doing?' for goodness knows what reason. ~_~ )
And then finally with KH 3 out expect years of DLC (Got a new Disney moving coming out that needs advertising? There's your new DLC summon.), post end-side stories ( maybe not even within the same genre, ala Dirge of Cerberus), trans-gaming content (animations, movies, ect.), and so on. They will do it; mark my words.