Alright guys, hear me out before you all go "but muh patterns" to mock.

In Gen 2, we got two eeveelutions, Espeon and Umbreon. Umbreon was a Dark-type, which is super-effective against Psychic types, which Espeon is.

In Gen 4, we got Leafeon and Glaceon. Glaceon was Ice, which is supereffective against Leafeon, which is Grass.

So what if the next eeveelution along Sylveon, if there is another, is Dragon? Fairy Types are good against Dragon.