The filed trademark by Bethesda parent company ZeniMax Media is “Dawnguard” — which may refer to the Mythic Dawn cult.
The Mythic Dawn were led by Mankar Camoran in The Elder Scrolls IV: Oblivion. They’re the same cult responsible for the assassination of Emperor Uriel Septim VII, and are obsessed with the Daedric prince of destruction, Mehrunes Dagon (also the main baddie in Oblivion).
We’ve seen Daedric DLC before, the ginormous Oblivion DLC Shivering Isles was dedicated to Sheogorath, the Daedric Prince of Madness, so this could entirely be possible. Give us your thoughts below.