If they are going to cut major storylines to trim the story, which might be better than trying to keep all major storylines but shortening all of them beyond recognition, the Seanchan one is an obvious candidate. Also because, well, so far they haven't exactly displayed the subtlety required to depict the good guys' relationship with the Seanchan and the whole Tuon situation in a way that makes any sense. And because they've been building up the Whitecloaks to be a bigger threat - so the Whitecloaks could replace the Seanchan in some aspects if need be.