The reason I'm bringing this up again is because I recently played through Shivering Isles, which in essesnce could be called a fantasy world within a fantasy world. What also struck me is how different the Shivering Isles looked like in contrast to Cyrodiil as far as the enviroment were. By having a daedric realm in Skyrim, that can be accessed at a certain point, could lead to diversity of the game's enviroment and keep it... "fresh" once the default of Skyrim would feel inadequate. It could either be in form of an expansion or already in the game, just being somewhat hard to reach. But that doesn't matter right now.
But anyway, would you like to visit a Daedric realm, and who's realm would it be?