Warning! Spoilers, or mayhaps just conjecture, regarding the previous and upcoming deaths of some characters...
Brian, it could be Jon and Arya.
I think we all agree Arya will go back to Westeros to unleash her killing powers. Will she still be associated with the Faceless Men? If so, then who would be her target or targets? Dany, Aegon, Tommen, Myrcella, Margaery, Cersei, Jaime, Tyrion, Connington, Doran, Arianne, Sansa, Littlefinger, and Varys could all either claim the throne or be the power behind the throne and thus are candidates for expensive assassination. Other candidates to upset plans for the Iron Throne include Stannis, Melisandre, Jon, Mace Tyrell, Olenna Tyrell, Roose Bolton, Walder Frey, and Euron Greyjoy. But what if Arya is working on her own revenge? The list grows smaller... Cersei, Ser Ilyn, Ser Meryn, Dunsen, and Raff the Sweetling (he will die soon) are the only characters on Arya's prayer list who are officially still alive. Of course when Arya finds out that the Hound is alive and the Mountain is now undead, she'll want them back on the list.
So if Arya is assigned the task of assassination in King's Landing, she might easily throw in a number of freebies as well.
What if someone contracted for Littlefinger and Sansa? What would Arya do?
What if Arya was assigned to kill Tyrion and Sansa, but found out that Cersei was the contractor?
As for the Jon, Tyrion, Arya triangle... Arya has shown herself unconcerned by physical deformity. She put up with Sandor for a long time. She unabashedly picked the grave worm from the old man's face. She's been friends with lords, ladies, butcher's sons, bastards, cooks, smiths, assassins, fishmongers, whores, and murderers. Young, old, hale, sick, rich, poor... Arya has known them all. She would not balk at dwarfism, facial scars, but what about necrophilia? I'm hoping GRRM draws the line there.
Jon already unknowingly carries a torch for Arya. He knew he was her closest family at Winterfell. She's the only one to whom he gave a gift. He constantly compared Ygritte to Arya, not Arya to Ygritte. He sent a rescue party when he heard she was back in the North. He forsook his vows for the second time (third time by Bowen Marsh's reckoning) in order to save Arya.
Arya already unknowingly carries a torch for Jon. He was her closest family. He gave her Needle... which she still has against all odds. She lost her father, her sister, her mother, her brothers, her wolf, her identity, her innocence, her friends, her place in life.... but she still has Needle. It is her one tangible link to normalcy, to who she was born to be, to who she was supposed to be, to the one remaining person who loves her.... the person who calmed her fears, the person who listened to her, the person who showed her it was okay to fight, the first person who believed in her vision of herself.
Tyrion does not even know Arya. But he'll be impressed when he finds out that she can look beyond physical and social trappings. That he could find a Stark girl who is not repulsed by him and because he has his own severe issues with his own siblings, Tyrion may find great appeal in trying to snub Sansa by replacing her with Arya. But all in all, I don't see a real connection between Arya and Tyrion.
I think Jonya is much more likely than Tyrya. Hey, if we can have power couples, then why not the Westerosi? I was the one who coined SanSan (Sandor, the Hound, and Sansa) back in '05-'06... and I have a sneaking suspicion the American tabloids stole BenJen from GRRM. Anyway, Tysan is more likely than Tyrya. But between Jonya and Jonsan, I dunno. But just remember.... the dragon has three heads... and that power coupling will be high voltage... Danjonsan? Dantyrsan? Hmmmm, what about DanEggSan? DanAriEgg? DanTyrJaim?
