1. Dawnguard
This Skyrim add-on DLC gave us a Vampire storyline, and if The Twilight Saga and Buffy told us anything is that people like Vampires (or at least stories about them). Serena is an interesting character and would provide an opportunity to go more into her history, and have a close relationship with the character, not as in a couple, but more than friends (but no benefits). I would have Jennifer Lawrence play her. Like with Shivering Isles, Dawngaurd offers multiple-choice scenarios, siding with the Dawngaurd or the Vampires, and another being whether to have your soul fractured or become a Vampire to enter the Soul Cairn. It might be better to agree on what will happen for the sake of making it easier to create episodes. A fan vote to determine what choices to be made, I would go for siding with the Dawngaurd and becoming a vampire to enter the Soul Cairn, and be cured later.