For Nynaeve, I submit Lucy Hale:
She's tiny, dark hair and eyes, is a little older than Nynaeve but looks way younger than she actually is, has the acting chops to pull it off, and can throw a temper tantrum like nobody's business.
They could probably trim the Shaido stuff considerably without much loss. The main storyline is important, but not only is the Perrin/Shaido stuff yawn-worthy, we really don't need hours upon hours of Sevanna and her Wise Ones being awful, either.
Also, all of the sniping between Berelain and...
One thing I'd really like to see is just casual existence of queer relationships. Replace the problematic idea of Pillow Friends with actual relationships between women in the Tower. Have some of the men who show up with their families to train at the Black Tower bring husbands instead of wives...