Is a Square Enix rep even plausible? I know they at least use to be on fairly good terms with Nintendo and even helped with one of the Strikers games. Not to mention a number of the original FF's being on NES. Plus, there's all the spin-off KH games & The World Ends With You.
To be perfectly honest, I'm surprised one hasn't shown up yet.
The most popular Square Enix reps for Nintendo fans would easily be Geno and Black Mage. I personally would love Black Mage to be added. He's my main in Super Smash Flash 2.
Although I would love Sora to be in the game (and I did vote for him), he wouldn't count as a Square Enix rep technically, as all of the original KH characters are actually owned by Disney.