Making an HD game is a very costly and time-consuming project. Somehow I just don't see SE greenlighting the project when Versus and XIII took so long to finish (with Versus potentially being another year or more away).
Square-Enix's HD games are not nearly as costly and time-consuming as the production time would lead you to believe -- Crystal Tools was incredibly expensive, for sure, but from what I've heard, most of the real work on XIII was done in a year and a half at the end, since they had only a barebones team working on the game while the engine was being created.
Besides, one has to wonder what they would have to add to make an HD KH game. They already
have super-high-quality versions of all of the in-game character models (
like so -- and there's one of these for every character, enemy, and NPC in the game), so it's not like they haven't been working with larger textures and higher-poly models all along.
Trying to imitate the CG renders might be more work, but it's also a terrible idea, because CG simply doesn't work for Mickey, Donald, and Goofy. Image quality is a much better place to focus on in a game like this -- KH2 looks amazing emulated with high levels of AA and AF, and it'd look even better with consistently-high-poly models and higher texture resolutions.
And, since the result probably wouldn't be taxing the system in any significant way, they could feel free to add in hordes of NPCs and more complicated enemies to make the worlds feel more alive. I'd like that a lot more than I would CG-style Disney characters, anyway, and it'd probably be a whole ton cheaper.