Brienne actually has a lovely ending as the head of the Kingsguard. We even enjoy the touching tribute she gives Jaime by preserving his legacy in the official ledger and finishing it with the words, "he died protecting his queen." However, I'm not a big fan of the way we left her at the end of episode four, crying over a man.
How about an ending where Brienne goes full John Wick? She could ride to King's Landing with the intent to kill Cersei for the indirect role the queen plays in destroying her heart. Yes, I am well aware that this is not in line with Brienne's honourable nature. But why should we let the lack of logic ruin our fun when the series has sidestepped this issue in the past?
Having Brienne go after Cersei would bring closure to her relationship with Jaime and force him to make a choice that's more difficult than simply walking away. Does he fight Brienne to save his sister, or does he side with Brienne to take down a tyrant? This would also give Cersei more to do than drink wine and look out the window all season. She'd either have to fight or use her cunning in new ways since Brienne only responds to honesty and a pureness of heart.
And of course, how awesome would it be to see Brienne charge through the Hound and the Mountain to slit Cersei's throat?