If she manages to kill off more of her enemies by infiltrating their ranks, she could take out some key players in the game.
After seeing Arya use her face-changing ability to annihilate House Frey, it really doesn’t feel like there are many limits to what she can pull off.
She can infiltrate just about anywhere, and she clearly hasn’t gotten over her thirst for revenge.
I’m not sure that a cliffhanger finale that reveals Arya on the Iron Throne before cutting to black would be what fans want, but it would definitely have people talking for years to come.