If there's one thing we can see from the end of Kingdom Hearts, Another Side, Another Story, ASAS: Deep Dive, and the numerous KH2 trailers, it's that there are clearly multiple keyblade masters, just as there are clearly numerous keyblades, as many as seven if I'm counting correctly, though I'm betting on there being five of them.

Besides, the story the old woman told Kairi about the keyblades suggested that there were two different masters, the one who brought light, and the other who brought destruction and darkness. If Deep Dive can be any indication, Riku seems to get a keyblade of his own.