I have been giving alot of thought to things i would love to see in a potential Skyrim dlc, that i believe would make the game, even funner than it already is!
Its kind of a List of things i have thought of, and things that i put together after seeing the Video of the week Bethesda let their Developers design whatever they wanted, and i love bethesda for allowing their staff to do that, that is a great way to put alot more creativity into games.

Ideas(Suggestions):
An Arena(Kinda Like in Oblivion): Much like oblivion the arena would allow you to Progress in Rank, like a faction, you would begin fighting npcs, but you would also be able to fight monsters, unlike oblivion, even after obtaining max rank you would be able to fight Npcs, Or monsters occasionally.
The arena could also have a type of prize system, in Oblivion you could only get Two Chest Pieces and Gold, i would like to see something like a Currency for winning, and gear you could buy with the Currency.(I Realize Arenas are kinda a Roman-Themed thing, but they are so fun!, one of my top 5 favorite things in Oblivion)

Redux of Vamprism:(Thought of this after seeing the "Ultimate Vampire form in the Bethesda Video), this would include Two new Factions, a Faction based on Vampiric Cult, that has a large variety of Vendors, and Trainers that deal with Vampires, and of course the new Last-Stage Vampire, this Faction would need to be easily accessible(Like in a city, or a cave with a Marker for fast travel), the Vampire Cult would have quests to Combat the Opposite Faction, which would be the Order of the Virtuos Blood, who would be the Anti-Vampires, they would set up a branch in Skyrim, the player would be alloud to pick either Destroying the Vampire Cult, or Destroying the Skyrim branch of the order, both with nice quests and prizes of course.

Beginning Stages of a Great War on the Thalmor: This is one of the ideas i had that would basically be Massive, i almost expect this to be a main feature in a future Elder Scrolls game, or possibly this is the DLC that is already in mind, it basically goes along with the storyline, though, it might not be possible if you side with the Imperials, but after the Stormcloaks take over Skyrim, the Imperials would notice they are loseing hold due to pact they made with the Thalmor, so they break it off, side with the Nords again and a new massive "Great War" starts.

Smaller Ideas/Suggestions:

• Add the Snow Footprints from the Developer week, i think they would give the game a even more realistic feel.
  
• Armored Horses(Or simply, new mounts): The armored horses would be stronger than regular horses, and cost more aswell, the armor would effectively increase their health by around 3 times a non-armored horse, so your horse stops dieing, the armor's color would be based on the city you buy it from.
  
• New Top-Level Armors: Blacksmithing made the game, really easy i think, i had Daedric Armor before i even began the main storyline, there of course would need to be new Light Armor, Heavy Armor and Mage Robes, possibly even weaponry, and i would advise or atleast suggest they are not craftable by blacksmiths, that or extremely difficult, like insanely difficult to obtain the materials for.
  
• Other Suggestions? Add almost everything in the developer free week video, your staff has amazing creativity, and it looked like alot of the hard work was already completed.

Important Thought:
If it is not possible to "Hotfix" specific bugs, a DLC would be the perfect thing to actually allow larger downloads to smash bugs that require more space than a Hotfix will allow, even though many people would possibly be angry they have to buy something to get bugs fixed, it could also be a free download called "Bug Fixing Dlc" or something, just a thought.