Today (Jan 29) the official Elder Scrolls Online Twitter and Facebook accounts have posted some short teaser videos. These videos depict a black mass, likely volcanic rock, with audio of rumbling and blowing winds. In the first video, it is merely the rock structure with a few embers appearing from within it. In the second video, the rock structure has opened a bit further, with more of its orange contents visible, and a date for a Twitch stream (January 31st, 11:00 AM PST / 2:00 PM EST) overlayed on top. A third video, posted on January 30th, has the same audio and footage, but more parts of the crack are filled with lava, and the phrase "Discover the Next Chapter" has been overlayed with it.
It is unknown what exactly the video shows, but the teaser is important enough that the official social accounts have changed their avatars to it, and pinned the tweet. Even Bethesda's twitter has pinned the tweet, so it must be something big for ESO. A blog post on the ESO Website says "We're revealing something big tomorrow that you won't want to miss." and that they will be unveiling "a bunch of new exciting, information". They also ask for those watching the announcement live to record their reactions.
There is no certain knowledge of what it means, but there is a lot of evidence that this is a teaser for the announcement of the Vvardenfell. This zone has been teased long before launch, and many files of the zone have been found in the game since early 2016, even an entire map found in the latest Housing update. Despite this, it has not been officially announced. If the video does indeed show volcanic rock, it is likely a Foyada channel of Red Mountain, the volcano on the center of Vvardenfell. However, it could also be one of the volcanos in the Spiral Skein, the Daedric realm of Mephala, which has been planned as a future location for quite some time.
With the Update 13 of the game being released as Player Housing for Q1 of 2017, whatever this teaser is, it is highly likely announcing the plans for Q2 of the year. Matt Firor will be posting his "Year Ahead" article for 2017 in the coming week, which will most likely also discuss the Q2 plans. May 1st of 2017 will mark the 15th anniversary of The Elder Scrolls III: Morrowind, and as May is one of the months considered part of the second business quarter, we might expect to see the Vvardenfell zone released on that date as a DLC. Be sure to tune in on the Twitch stream this Tuesday!