Bethesda reckons that details about Skyrim DLC could be released as soon as "next week"... but an intrepid Bethesda forum member has discovered some exciting potential tidbits that might shed some light on what to expect from the mysterious expansion.
An asset folder entitled DLC01 was discovered within the latest update, which is suggestive all by itself. Upon further inspection, however, this folder contained crossbow animations, assets for Snow Elves (including fireballs and a Snow Elf prince, no less), and new vampire feeding animations. In case you don't know, the Snow Elves were a proud race driven into slavery and barbarity by the duplicitous Dwemer - and they've certainly been fleshed out with plenty of backstory via a couple of quests, dialogue and books. They now exist as the blind Falmer, a shadow of their former glory.
A Snow Elf prince already features in Skyrim's lore, described as "an Elf unlike any other" whose fighting prowess won him the respect of the Nords. He currently lies buried beneath Solstheim: the snowy island that played host to Morrowind's Bloodmoon expansion. Interesting.
Considering that Bethesda recently trademarked 'Dawnguard,' the next DLC pack appears to be falling neatly into place. We'll have to wait and see.