M.G. Siegler had a terrific suggestion for making Littlefinger’s death more meaningful and interesting:
In the scene itself, as Sansa calls out Littlefinger as the conspirator, rather than having him grovel as he does before dying, I would have had him play his one final card: he knows that Jon Snow is not a Stark. As Arya draws the blade, he could let slip that “Jon is not your brother” to not only Sansa and Arya (who still do not know this) but also to all the lords in Winterfell who are present to overhear. This plants a seed in the head of the girls, but more importantly it calls into question the leadership of The North.
Littlefinger’s demise was particularly pathetic: it made little sense as to why the Stark women acted as they did, nor was it apparent how Littlefinger managed to lose everything so quickly given his own planning and resiliency. Had he at least inserted a final barb as he died, the viewer would have the pleasure of watching the effects in the final season. Unfortunately that’s a lost pleasure so we’re just left with are dragons, the dead, and (almost certainly) betrayal and mayhem.