Tyrion: Jon is King in the North and, after Daenerys retakes King's Landing, writes to her to negotiate for peace. Daenerys brings Tyrion with her to Winterfell to treat with Jon and Sansa, as Lady of Winterfell, has to interact with Tyrion for the first time since the Purple Wedding. Their connection starts out stilted but grows stronger as their monarchs negotiate.
Sandor: Sansa flees with Sandor during the Battle of the Blackwater and, instead of heading North, they escape to Essos, carving out a life with each other there while keeping an eye on Westeros to gauge when it would be safe to return.
Baelish: Baelish leaves for the Vale shortly after Jon is crowned King in the North. Sansa, after getting a taste for vengeance after dispatching Ramsay and generally growing bored with life as the Lady of Winterfell, is in a much more receptive mood when Baelish returns to Winterfell while they are preparing for the Battle for the Dawn. The catch: she wants to be an equal partner in his schemes.
Willas: The Tyrells whisk Sansa off to Highgarden before her marriage to Tyrion and a sweet, uncertain courtship occurs between the crippled Willas and the anxious Sansa. They attempt to weather the war together but, when Olenna declares Tyrell for Daenerys after the sept explosion and Daenerys starts to re-conquer Westeros, including the North, Willas and Sansa attempt to mediate between the Dragon Queen and the King in the North.
Harry: Lord Robert dies, leaving Harry Lord Protector of the Vale and Warden of the East. Now that Baelish has lost a good portion of his power, Sansa reveals herself as Sansa Stark to Harry and becomes the Lady of the Vale, dealing with Baelish, Jon, the War for the Dawn, and, eventually, Daenerys.
I also have ideas for Jon. Threading only, three to four paragraphs per tag. Looking to do a lot of world-building and take things to the ultimate conclusion of the series, just our own conclusion instead of GRRM's. :D