Nomura said the the menu screen for Re:MIND(which featured Sora and Kairi) was the basis for one of the upcoming games. And if Riku is still involved based on the secret ending then the Destiny trio could be together in ShibuyaWell Kairi and Lea will probably be a team. lets also not forget Ven Aqua and Terra.
However what do you mean they are getting their own game in the form of DDD volume 2? Did I miss something, is that the game coming out before KH4?