Pretty sure I seen somewhwre that a new landmass is added around Solitude, supposedly where castle Volkihar is. That is just speculative at best but I thought I might have seen it in an interview. The other new area is the Soul Cairn.
Speaking of the Volkihar, I was playing today and was doing the quest ''A daedra's best friend'' and the first place Barbas takes you has some Volkihar vampires, the location is also on the coast of skyrim...