I think Sansa goes through her own wildling arc in the Vale (parallel: Jon and Tyrion). I think the mountain clans attack the tourney. Similar to the fighting pits where the stage fighting became real when the dragon showed up, I think the tourney will go from chivalrous sports event to a deadly battle very quickly. This event also explores the consequence of Tyrion arming the mountain clans: they're much more deadly and bolder now.  Then I think she'll be stolen by one of the clan members