If they do werewolf Sims right (not the big puppies they were in Sims3), I think EA might recover from the MFP Stuff Pack embarrassment!
Alternately, either Witches (another of my fav) or Fairies (very close runner up)!
As an example, I took one of the Sims3 townies (Sunset Valley's Zelda Mae) and made her a fairy... just maybe not the way you'd expect -
NO dainty fairy here!
http://i.imgur.com/Uh2jYRp.jpg
If they give us the Fairies, hopefully they put as much effort into them as they did the Vampires. Let it be so you could customize/custom color (or both) the wings, like you can customize Vampire fangs.
http://i.imgur.com/L0kSuWZ.jpg
Let them have their FULL magical powers that they can create havoc and pranks with. Nothing was funner than using magic to have bees attack someone going to get their mail. Or better was transforming a Sims face to look hideous (for 24 hrs), to teach them to be nice to others.
http://i.imgur.com/BLm2388.jpg
http://i.imgur.com/ERirIzI.jpg
And Dear God - Let them be able to fly and hover, because it'd be pointless for a Fairy to have wings, if they're just gonna walk EVERYWHERE!
There's been a lot of changes at EA since Vampires came out. So there's no way of knowing what creative minds may have come and may be gone by now.