I've kinda been wondering about KH3, but from the other end: We know from the ending of KH2 that if people don't mysteriously dissapear, you'll have five (or seven) keyblades floating around the party. Sora can wield dual blades. Riku can wield dual blades, but doesn't in the game because he gave his second to Kairi. And if the blade stayed with Kairi, that means she can wield a blade too, it just hadn't come to her yet.

Sora and Kairi's nobodies, Roxas and Naminé, apparently can manifest independantly of them despite having been retuned to their progenitors (q.v., again, the ending of KH2). Roxas can wield a blade when independant of Sora, so it would be reasonable to assume Naminé could as well, once Kairi's keyblade manifests.

What in the world are they going to do with (potentially) seven keyblades floating around in the starting party (plus Micky's wherever he's at by then).