I can't imagine why they wouldn't case a black woman to play Tuon. I am sure other characters could end up being case as epople of color even if the book character isn't. I mean, is there any reason Berelain couldn't be a beautiful woman of any race? Fans always holler and cry if the person cast...
I think Alycia Debnam Carey could play a pretty good Egwene. When you see her as Lexa in The 100 she is total badass, but at the beginning of Fear the Walking Dead her character is very naive, so she does both really well.