Many ideas have been bopping around that the new secret ending takes place in Castle Oblivion, as a Memory of Xehanort reborn by the Castle's memory-showing rooms.
We have also seen a place in the PV that looks exactly like Castle Oblivion (in KHII) called the White Place. This could be linked to CO, and allow us to travel into Xehanort's memories and fight the AU.
We have also seen a place in the PV that looks exactly like Castle Oblivion (in KHII) called the White Place. This could be linked to CO, and allow us to travel into Xehanort's memories and fight the AU.