As much as I love many of the GOT cast for WOT parts I would feel dirty and maybe even a little cheated if they used any of the big characters. I just know non WOT readers watching are gonna think oh its just a copy paste of GOT.
I'm reading Crossroads of Twilight right now and for some reason cannot get the image of Melissa Mccarthy as Arymilla out of my head. She has lost quite a bit of weight and fits the plump but pretty really well and can pull off looking vacuous.