I am one of these people. My game choices are souly based on plot line and then graphics. If your game is younger than the year 2000 and has crappy graphics, I'm sorry but I will not buy your game.
KH3 will be a Square-Enix epidemic (when it's finally released). Who knows- by the time it is released SONY could have a whole new console out and it could be on that platform only (I wouldn'tput it past them *Cough* KH
DD, BBS *cough*).
But yes; I feel that the cut scene graphics will be similar or maybe even better than the BBS ending cut scene.
Game play however I do not think it will change too much from the graphics of KH2, as incorporating so much detail into characters and scenery that gamers will want to either a) fly through or b) interact well with and have smooth play is kind of pointless as it will take longer for the game to release and will make it hard for the programmers to animate the characters and give the player free-will over their actions.
These are my feels, add your own.