GRRM has been building to something in the Vale, as well as introducing/building characters and the way they interact. Unless he introduces another POV in the Vale (unlikely), then I don't think he'll be moving Sansa out of the Vale until some significant things happen there. In fact, I'd be surprised to see Sansa in KL at all (been there, done that... why set her story back a whole book?) However, there's a chance this situation could work with Jaime being needed to save Edmure for instance. Or perhaps for Jaime and Brienne to do at the Twins what Jorah and Barristan did at Meereen. It's hard to say, because neither UnCat, Jaime or Brienne seem to have reached any sort of natural conclusion in their overall stories.