I don't know if this is helpful or hurtful to the case towards Kairi starring in her own game... or heck, even being playable! But of the characters on the cover of KH3, it is only Kairi and Namine who haven't been playable at some point. Sora, Riku, Terra, Ventus, Roxas, Aqua, they've all clearly been protagonists of their own games. Mickey was briefly playable at times in KH2. And then Donald, Goofy, Axel, and Xion (and Mickey as well) were all playable in Mission Mode of Days. What does that mean for Kairi? I think it means that she's almost never considered a fighter, at least not enough to ever be playable. And I think that might hamper her chances of ever getting a game.