Even if there is a big twist it's still just one ending...?
Maybe, maybe not, we'll see. Morrowind and Oblivion had only one ending, will Skyrim continue the trend? What we must consider is that Bethesda most likely intends to continue the Elder Scrolls series after Skyrim, and when you make a sequel to a game with multiple endings, there's the dilemma of how to reconcile the multiple endings with the series continuity. Some games find a way to make it so that all endings could potentially happened, and some series just assume one ending is canon, some games might use the Mass Effect route of checking for a save from the earlier game, and changing the game based on your choices in that save (Of course, if you completed the game but already deleted your save, then too bad, you're going to have to go with whatever outcome the developers decided to make the "default" one if you didn't have a save to read.) The last time an Elder Scrolls game had to deal with this was Daggerfall, for which Bethesda had to introduce the Warp in the West, thus making it so that ALL the endings were canon, but it's going to look pretty silly if after every game you have some crazy time screwing going on. On the other hand, with the main antagonist of the game apparently being another aspect of Akatosh, I think Bethesda could justify a Dragon Break happening after Skyrim. Will they use this to their advantage, though? We'll see.