I think they should add a new dlc where a necromancer reanimates all the npcs . Well only the ones that that the player was responsible for their death. Perhaps even a few bandits and forsworn. For example their could be an area were Cicero (the joker from the dark brotherhood)( if you killed him) wants revenge and challenges him to a battle along with help from old dark brotherhood members or bandits. Maybe even Grelod the kind could be there.
I also think a DLC involving forsworn. Like maybe the player gets a letter from the Jarl of Markath about the forsworn taking over. The player then goes to Markath to find the forsworn already have taking over. I don't think It should be available to fast travel to Markath. Until finished.
My final suggestion is a small DLC where your followers can do more things. For example: You are wanting to join the college of winterhold and you pass the test. Your follower than says to you he/she wants to join too. If he/she doesn't know the spell for the test ,they'll ask you for the money to buy the book for the spell. The player can then do quests while the follower acts like he/she is actually a student and will where the novice robes during the questline. Or maybe after finishing a battle that lasted about 7 or more min than the follower will say whoa that was quite the battle. Or maybe if your the arch-mage you can recommend her/him to join the college or the companions. If you tell your follower to kill a innocent person they say " um.. alright." or something else. If he or she/he does it you can recommend the dark brotherhood.