Nomura explained that Sora and Riku appearing as they did in KH1 in 3D is essential to the game's story... and I think it's essential for KH3's story as well. Think about it. This game will probably give a reason to why Sora will be at level 1 in this game AND in KH3. Obviously, we don't know how or why story wise they appear this way, but in terms of gameplay, i think it actually is necessary.