I'll go first.
After uniting Skyrim by convincing both Imperials and Stormcloaks he was on their side and using the opportunity to kill off both, The Dragonborn then starts up a Skooma ring. With the Thalmor getting int he way of profits, he decides to throw them out of Skyrim once and for all, but on his way to the Embassy, an ebony clad Bosmer warrior appears. He calls himself Gaenor, and says his spirit has been rematerializing a long time after his defeat at the hands of The Nerevarine. The Dragonborn finds himself severely outmatched and falls to Gaenor's sword.
If Bethesda isn't going to finish it, I can imagine anything I want.