It goes so far back, Nomura said, that it began before Kingdom Hearts was even conceived. So if you're seeing a bit of keyblade armor in there, that's because the canceled project went on to influence the Disney series and its armor design, and not the other way round.
"Many years ago, I worked on a different project and the [figure's] concept and idea was kind of already there," Nomura explained. "Unfortunately, that project didn't pan out and it never saw the light of day. When the merchandise team started expanding into the DC Comics Variant figures, they approached me and said, "We remember you drew a sort of Batman design back then. Would you be able to share that with us?"
The Siliconera interview also goes into the process of designing and creating the figure - apparently Nomura and his team had to come up with a backstory for the figure. If you're curious, that backstory will be revealed at a later date.
In the meantime, Square Enix is showcasing Nomura's Batman at the San Diego Comic Con this weekend, As Siliconera posted, one of the display units at the convention simply bears the word "next" with some kitty paw prints along it. That's a clue for the next of Nomura's Batman figures, and we won't need Adam West's help with solving that particular riddle.