I will add to it with time because you know, it's Game of Thrones
  1. I want Arya to kill Cersei by pretending to be Jamie.
    Let Cersei think she is experiencing the ultimate betrayal and at the last minute, right as the life is about to leave her body, Arya reveals that it's her. No words, just staring her dead in the eye as she takes her last breathe.
  2. Khaleesi/Arya power duo.
    They would butt heads a lot and Arya would have a hard time bending her knee to any sort of ruler but I think that she could bridge the gap between Dany and Jon. Tyrion could convince Dany to trust Arya so that Arya could convince Jon and Sansa to trust Dany and together they can all fight the White Walkers, as one big, disgruntled, mixed family.
  3. Sansa NEEDS to kill Littlefinger.
    Kill Littlefinger, marry her cousin, take the Vale, make Jon reliant on her army, start calling shots, be a badass, (get me all the fantasy points).
  4. Littlefinger will try to use Sansa and Sansa will use him like a wet rag and RULE