i disagree personally and i think that they can add a quest line that doesnt require you to become a either a vampire or a werewolf to participate and contracting the curse would happen either would happen in sleep or in a random encounter without the questline. It should just be a illogical hatred turn both factions or better just a rivalry between 2 groups with around 7-12 npc members each (thats alot of writing and voice acting) i think a small group like that would be ok because it wouldn't interfere or compete with the main storyline and it can be done the same time anyother quest. NOTHING LAME like that twilight romance crap, im talking real monsters battling it out for pray and unreasonable dislike for each other.
If Bethesda only has time for one i think werewolves would fit in better then vampires, wolf running in the snow n all
anyone else want werewolves vs vampires in skyrim? i know im not the only one >.<