I tend to take Graendal at her word and RJ at his when they express that she doesn't know who or where he is and the latter indicates there is no information we would have access to allowing us to figure this out.

I think he is just a lame duck, like many of the Forsaken. He seemed so infantile at the meeting towards the begining of the book that I think we may as well keep on the lookout but not be too surprised at how he falls. He seems more similar to Lanfear than Moridin in many ways. He's more dangerous than Mesaana but he literally broadcasts the ring in his nose that can be used to pull him. Let's get this straight: Semirhage is captured and now in big trouble because she injured Rand when those weren't her orders...and Demandred basically blurts out that he will be the one to kill him in front of Moridin. What a maroon. Pride tends to go before a fall, and Demandred has more than enough for any man.