As a PlayStation-centric site, I'm not even sure we should be reporting on this. But dragons are involved, so…
One nosy gamer in the Bethesda forums has gone through the game's 1.8 patch source code and in doing so, has found a few references to "Dragonborn" and "DLC2."
The user also said the expansion will give us new armor types, and may actually allow us to ride dragons. The latter is by far the coolest part of the theory, isn't it? Evidently, the setting may be the island of Solstheim, which is northwest of Wardenfell and east of Skyrim; if it's an island, it'd make sense to be able to fly… It should also be noted that Bethesda parent company Zenimax Media filed a trademark for the name "Dragonborn" some months back, so this is a definite possibility.
The DLC is probably coming although admittedly, we're not sure about the riding dragons part (no one is). PS3 owners may not care, because they're probably convinced they'll never see this expansion, anyway. Bethesda hasn't managed to deliver any other Skyrim DLC to Sony's platform yet so why should that change for Dragonborn?
Related Game(s): The Elder Scrolls V: Skyrim