Following some nifty datamining of the game client last month, the next Skyrim DLC was outed as Dragonborn. You can also find a good round-up of info that was gathered here in the Bethesda forums (spoiler alert!).
This evening Bethesda posted a short and to the point Tweet stating that a trailer was being released on Monday. We don’t know when, but it is coming. A teaser image has also been posted, not that it tells us much.