The Riverlands are going to be interesting. Arya is there, with a mask, her destination "west of Westeros." But checkout the names left on her list:
The Hound, Cersei, the Red Woman, Beric Dondarrion, Thoros of Myr, and Ilyn Payne
The Hound, Beric, and Thoros are in the Riverlands, and the Red Woman is heading south. Doubtful that Arya wants the Hound dead. His desire for revenge combined with Arya's list seems to make them natural allies instead against the Brothers Without Banners/Lord of Light people.
Nymeria's superpack was said to be in the Riverlands too.
And I forgot this but in Dance with Dragons (ch 3), Jon has a dream that he is Ghost, and being called by his sister "with many cousins" from the Riverlands...