I personally don't trust KHU on this one. Kingdom Hearts II isn't out yet, so we have no idea what will be left of the storyline to continue on from. If there isn't enough left to move forward, there can't be a "true" Kingdom Hearts III -- though a spin-off would still be possible. It's also suspicious that, despite saying they'd have it translated, they have yet to do so. No one else has bothered to translate it, either.
The only hint Nomura has ever dropped about another continuation is the yet-to-be-revealed "strongest" character in the series. But granted that was before Xaldin was revealed, so the strongest character may just be in Kingdom Hearts II, thus ending the series with his/her defeat, or perhaps even the death of Sora himself.