My speculation for the next Square Enix character; based on sales, popularity of games, popularity of character, relations to Nintendo, character future, representative of Square Enix and current relativity. I would have to say its between Sora and Laura Croft.
They have a high popularity and stay current due to them being the protagonist of the many games they appear in. If either of them made it in, they would represent not only their games, but Square Enix as well. I did not choose a Dragon Quest character or Crono, due to the fact that Dragon Quest has many characters. And Crono is not that relative anymore compared to Sora and Laura Croft.