Bethesda has announced the imminent arrival of a trailer for the next Skyrim DLC, but that hasn't stopped the speculation.
All we have officially to tell us about the next Elder Scrolls V: Skyrim DLC is this image at right, showing what looks like a new armor set, perhaps a metal set in the Falmer style, or perhaps chitinous with a metal plating.
It also looks suspiciously similar to Dragon Priest armor, so it might be a derivation, perhaps from a sect which has been long separated from Skyrim, showing, perhaps, that this DLC will give a larger land to explore in addition to Skyrim itself.
I wouldn't think that it might be chitinous except for the wild speculating that's been going on in the Bethesda forums, where members have cracked open the source code for the most recent update and found the code for several new feature which have yet to be announced.
Within those cryptic lines, the fans have found references to a title, Dragonborn, hinting that the next DLC will take place after the main quest line is complete, and will introduce some new facet of what it actually means to be a Dragonborn. This might be just some new plot points, but further speculation is that it may be a new skill tree which will allow the player to develop their shout skills and other Dragonborn properties.
There is a list of new armor types, which is what made me think that the armor in the teaser pic might be chitinous. Players will be able to wear and craft Bonemold, Chitin, Nordic and Stalhrim armor types, all with light and heavy versions.
References have also been found to new animations which include attacks with spears, and dragon riding, leading many to believe that players will now be able to tame and ride the dragons. Of course, the forum users head off on wild flights of fancy about how great that would be, but one should not get one's hopes up. It might just be a new cut scene or canned sequence, in which the player rides the dragon as a quick-travel mechanism.
Actually flying around Skyrim, and fighting from dragon-back is incredibly unlikely, especially considering the number of other changes to the game would have to be made. For example, currently, the major cities are separate cells in the design of the world, and if you were to fly over them (like, with a cheat code or something) you would only see the rough outlines of the city's buildings - so that it looks okay from a distant mountaintop - but there would be no people or actual interactive or destructible objects. That's just one example of an issue free flight would create in the engine of the game. The addition of spears as a weapon type sounds intriguing, however, and perfectly plausible.
The most interesting that the users have found, however are references to locations that give some clue as to where the DLC might expand the explorable territory of the game into. The locations mentioned are Raven Rock, Miraak Temple, Castle Karstaag and a Telvanni tower, all places that you would find in Solstheim. Along with them are a few new location marker illustrations, shown at left.
Solstheim was also the setting for the Blood Moon expansion for Elderscrolls III: Morrowind in which the major feature was the addition of werewolves, including the ability to be one, similar to the way Dawnguard introduced Vampires to Skyrim.
As I said none of these details are confirmed yet, and we can't even be sure that all of it will be proved or disproved by the rapidly approaching teaser.
No release date has yet been announced for Dragonborn, but I wouldn't be surprised if the expansion comes on December 12, 2012, since the base game was released on 11 November, 2011.
Update - November 5 2012: No need to speculate further. The trailer is out now.