With plenty of possibilities being thrown around, I haven't seen one that considers the newcomer being a dual-type. Maybe one was made and I didn't see it, but whatever. Despite the previous Eeveelutions being a single type, I personally don't doubt the possibility. Then again, I don't doubt a new type either. We'll just have to wait and see how that goes.
Ninfia being Normal/Ghost would make it seem like a sort of holy being, only succumbing to the darkness, yet shrugging off the assaults of other spirits as well as fighters. It's a combo that hasn't yet happened, and on Ninfia, it makes sense. Besides, who said Ghosts have to look scary?