They would be a great addition to the game because it doesn't force players to be a normal "hero" which is the CLICHE for all ES games. There has to be something the player can turn into and be a supernatural "abomination" that eats people or svcks their blood. Frankly, if they don't add werewolves or vampires I would be extremely dissapointed. I wouldnt even buy the game, unless they add the ability to cannibalism on a human flesh or be a Lich and svck people dry. Then I would consider buying it.
agreed, this is just something TES has to have to be true to the freedom they say they provide, werewolfs and vampires are a way for the player to choose a truely evil path with some intresting transformation/feeding options. I believe skyrim has them because if they didn't then todd and the rest of the dev team has their head up their ass, its something that a large percentage of the fans want and if they want to build a bigger fan base and make more money then why not ride the twilight train and just give the fans what they've been asking for, werewolfs and vampires. Its so easy to see that if they leave them out then they lose a part of there fanbase, and possible have other fans not trusting the company to come through with their own request.
I mean seriously, oblivion got ate up by the werewolf fans alone on forums/e-mail/mail/twitter/etc.