I'm guessing Kellhus is possessed by someone blind to the Inchoroi, and that certain someone is the one asking the questions in bold. I don't think it's a coincidence everyone has been calling him a demon. They're calling the spymaster Iyokus a Necromancer, so maybe he summoned Kellhus back to the real world via Daimotic sorcery after he went to Outside. Perhaps we'll have confirmation for it through Meppa, since it has always felt to me that it was portrayed that the Cishaurim were the most correct about things.
Uh, I'm expecting a re-match between Mekeritrig and Kellhus. It has to be done. Another thing from the first book I'm expecting a throw-back to (since it is the the last book of the series, and it is Fantasy after all), is to the origin story of Ishual. I'm guessing it will be some sort of a parallel with the not-so-right Anasurimbor kids. Maybe Moe Jr or the Crabhand-Kid. Perhaps the Crabhand-Kid will find his way back to the ruins, meanwhile a world-ending battle will take place, and some remnants will find their way back there. Something like that.