I've gone through the Civil war quests at least 6 times, 3 for the Imperials and 3 for the Storm Cloaks, and both Ulfric and General Tullius both made mention to a larger more powerful enemy - the Alemeri Dominion. Even when Tullius' on his knees he tells Ulfric that this "rebellion" was made so that Skyrim would be weaker and good soldiers would be lost and that they could take Skyrim with ease. Ulfric mentions in his speech that they will fight the Dominion in Skyrim or abroad. Tullius' speech is nearly similar saying the next target of the Empire is the Dominion as well.

So from all of this information, I've come to the conclusion that no matter which outcome from the Civil war a new questline will prevail through a DLC. We might see ourselves going to the Dominion itself in the Summerset Isles, or just staying in Skyrim and facing them. Going to the isles seems more than appropriate for a large scale DLC like the Shivering Isles the Empire or Stormcloaks could set sail and attack the Summerset Isles head on or some other way. But I believe that this could be a DLC in the near future.

What is your input on the matter or views on what the next DLC might be about, I could be wrong they might just relase a few smaller scale DLC like Mehrunes Dagger or 2 fortress DLC in Oblivion.