Well... I have been think about this for a while, as the central point for a DLC, you'd go into a Dwemer dungeon, then aways down there would be this room with a giant metal Dwemer head with a mouth opened in the shape of a door, no door inside, and it'd be kinda shallow. There would be a large empty pedastal, and Dwemer mechanisms, all in a general state of disrepair. There would be a man studying the machine, he'd be some scholar, who'd be a generaly swell guy, he'd explain that he belives that a small group of Dwemer fled to (Insert plane of Oblivion here), and that this machine opened a portal to it, he would then ask you to gather him a few ingots, some scraps, and maybe a few parts, to repair the machine, then he'd say he needs the activation gem that fits on the pedastal, he'd explain that he belives Falmer in the lower levels have taken the gem, he'd locked the door (with a key) to the lower levels and barred it, to keep the Falmer from getting him, he'd hand over the key, and you'd head down. After many annoying high-leved Falmer battles you'd find the gem, and head back up. The man (From now on I'll call him... Um... Uh... Jornd Vercius (Imperial-Nord :D)) would activate the portal to (Insert plane of Oblivion here), Jornd would ask if he could come along and the search for the lost tribe would begin, of course the surviving Dwaves would be mentaly warped from their long stay in (Insert plane of Oblivion here).
Just have to decide which Daedric Prince (And it's plane of Oblivion) for this DLC to be based around. Oh, and a catchy name that's actualy two words, but just without a space.
Dawnguard - Molang Bal
Hearthfire - ????? (Haven't realy used it) (It might not have one because it's not a full DLC)
Dragonborn - Hermaus Mora