Am I the only one that thinks the player might get the X-blade? Like out of everyone they are the most worthy of it, they have been to the Realm of Darkness increasing the darkness within the player, yet the light of the player should make it in an equal state. Thus allowing them to summon the X-Blade, so maybe they summon it during the Keyblade War and use to to survive the slaughter of all of the keyblade users fighting. Because I doubt that the Player is even skilled enough to be the last one standing.
I don't even think that dream depicts them being the "last one standing", rather, they are one of the last few standing. Besides, if they were to wield the X-Blade, there'd be too many plot inconsistencies if Xehanort refers about the history of the X-blade in Kingdom Hearts III.