Mr. Scott, I remember, said that the two title characters in the last two books would be one we had already met in a book previous to The Warlock and one would be one we met in or after the Warlock.
I doubt he would name a book after Josh, and not for Sophie, so my vote goes to Sophie for enchantress - beside the point.
So, I believe that The Warlock is someone we met in this book, hence, I came to the point of Aten.
Unfortunately, I don't think someone new deserves a title and I hope I'm wrong. I believe Mach, who has been in it since book 2 deserves one.