I like this theory. Personally i think the new KH will take place in the realm of Between/Nothingness/Twilight/whatever. I think so because the sky in the KHII and KHIIFM+ secret endings is like the one in twilight town. I agree with the next game being about Xehanort, it would be really cool and Xehanort´s memories are the biggest mystery right now.
Thanks, also I agree. It may be in twilight town or in the sam realm, such as an inbetween word. That would make more sense.