Although I'm not sure it would make a Good DLC, I wish there was a "Lawful Good" faction in Skyrim.
I know the Main quest is pretty heroic, and there are snip-its of quests here and there, but there is no real "Temple" faction or "knightly/Paladin faction".
The Mage College is good, but more of a Magical research type of thing. The Thieves Guild and the Dark Brotherhood are as they always were, and the Companions would have been a Great heroic Faction but it gets blotted out abit by the whole "Werewolf" thing.
I always wanted another way to play the game diffrently, like a Paladin/priest'ish faction. You could take quests from the diffrent temples to Help the Hungry, heal sick children, sanctify homes, exercise evil places
..and Of course, my favorite, protect the chastity of Dibellan Priestesses. ...
Oh-la-la
I would say again that I'm not sure something like that would go over as a Good DLC, as much as it should have been in the game to begin with. When so many people have been playing as Assassins and Vampires, I'm pretty sure that right when a "Lawfully Good DLC" came out, you could hear millions of 14-year-olds across the world simultaneously shout "OMG That's SO G*Y!!!!!"