The idea of shifting the paranormal fasciantion from vampires to something like zombies is logical and probably natural. However, zombies will never have the romantic appeal vampires have always held. Zombies are undead creatures, mindless and brutish. Where is the appeal in that to a teenage girl? But take a vampire, always painted as hauntingly beautiful and tortured, and you'll keep the interest. In order for the focus to shift off vampires to another mythical creature, that creature would have to be one just as appealing. Zombies and werewolves don't really have that, unless shown in a humorous way.