I would really like to see a new Eeveelution introduced. They already have Water, Electric, Fire, Psychic, Dark, Grass and Ice types.
If there was another one introduced, I would be absolutely amazed. I'd like to see an Eeveelution that is a Light-type (if it's ever introduced) and called "Stareon". But if not, then there's potential for uses of other types as well, such as Ground-type.