[Seafoam]

Spoiler for Don't read this if you don't want to be spoiled on back cover:

Spoiler for Seriously:

So the master of masters created "Xehanort's Keyblade" in order to be able to see beyond his death. He used his literal eye to do so, and tasked Luxu with finding a successor. The keyblade has to keep moving to next wielders for it to be relevant in the future. He also created the Book of Prophecy. But Luxu doesn't get to see it or get his own because it would create a time paradox.

Seeing as lots of dark keyblades in the series have a blue eye on them, like Riku's, Vanitas', and even the one Terra gets right near the end of BBS, this is probably all connected. I think we have a strong likelihood of the master of masters either being relevant in KH3 or the next saga, most likely as an antagonist.