The Demandred identity debates were premised on one of the big secondary characters being revealed to have been Demandred all along, like Talmanes, or Mazrim Taim, or Davrim Bashere (all of whom were contenders at one point or another). The fact that Demandred was hiding as someone who hadn't been "seen" in the books prior to Knife of Dreams, and that he hasn't revealed himself prior to the last book, pretty much makes it irrelevant. Demandred was the gun on the wall that never went off, a major let down in a series of disappointments that have caused this series to slouch to a somewhat predictable and formulaic end.