So, Kairi's heart goes into Sora; Naminé is created. Sora loses his heart; Roxas is created. But, when Sora releases his and Kairi's heart, what if Kairi's heart became "attached" to Sora's body somehow? Do you think that two Nobodies were created? Kairi's heart - Sora's body; Xion has traits of the opposite: Kairi's appearance, Sora's ability to wield the Keyblade. Just some speculation.