I'd love to see some recurring characters from previous games. I only picked up the series from Morrowind but I think they could put any of the memorable NPCs into TES V. They could be ghosts, undead (vampires, werewolves, etc.) Daedra, or even some mage who's keeping him/herself alive using magic, but they can also be relatives of past characters. I'd like to see Vicente Valtieri return and this time around he can be the Listener in the Dark Brotherhood and can also be an uber powerful vampire...which then gives the PC an option for entry into the Dark Brotherhood as well as the chance to become a vampire (by choice anyway). I know it sounds similar to OB but it kind of makes sense to me that Valtieri would still be alive, be even more powerful than he was in OB and would have taken over the Dark Brotherhood after the hero of OB died. Either that or he could be the leader of his own coven of vampires which you might stumble upon in a cave or cavern while exploring and which you could become a part of and use that coven as one of your "homes".
Also, I agree, relatives of Adoring Fan, Fargoth and Glarthir would be hilarious! Fargoth's relative should still have Fargoth's ring, with a backstory on how it came to him. Short of another adoring fan, maybe they can have an adoring mudcrab that follows you around but is not as irritating as Adoring Fan was.