I was recently playing and came across a book in the game where the cart is overturned and the woman is dead just southwest of Dragon Bridge. There was a book called "Immortal Blood" (which I know you all are probably familiar with) in which there is a story about a vampire hunter. Now I have a PS3, so I haven't played Dawnguard yet , but I know the name of those vampires from the previews and the book talks about the Volkihar vampires of Skyrim:

"the most powerful tribe, the Volkihar, paranoid and cruel, whose very breath could freeze their victims' blood in the veins. I explained to him how they lived beneath the ice of remote and haunted lakes, never venturing into the world of men except to feed." and also, "Your advice helped me very much," he said. "But you should know that the Volkihar have an additional ability you didn't mention. They can reach through the ice of their lakes without breaking it. It was quite a nasty surprise, being grabbed from below without any warning."

I have two questions:

1) Is this a fairly accurate description of these vampires from this book? (again, I don't know since I'm on PS3, and I don't want to know spoilers)
2) I think it could be very possible that Bethesda has included clues about all potential DLCs in various books around Skyrim. I mean, "Immortal Blood" has been a book since Skyrim first released and they at least took the idea from it. So, is it possible that there are other books which we may have paid no attention to previously that may actually contain clues to future content? I am going to start reading books I come across in game to see if there is anything that seems feasible.

Have you all found anything?

I think you are correct in your assumption and I have it on good authority that the next DLC can be "previewed" by reading The Lusty Argonian Maid...

I smell some Hot Coffee brewing...

Immortal Blood was also in Morrowind and Oblivion. But nothing came out of it, just in Oblivion was a vampire hunter's "guild" questline.

I know Immortal Blood was in Oblivion, but I don't remember it being in Morrowind. Either way, it's just a book that coincidentally talks about vampires that eventually become part of a DLC. It also mentions Movarth, who was a vampire in Skyrim itself. I mean whatever the next DLC is might be in one of the books, but probably only because it is based in the lore, not because Bethesda is hinting at what it will be.

Immortal Blood is an old book.

You are probably right, but it would have been really clever for them to place hints in Skyrim books or take ideas from older books. It makes you wonder exactly how far ahead they plan these things...

I think a lot of the quests and possibly upcoming DLCs are based on lore from books. If you read a lot of the books, you'll realize that there's a lot relating to them.