Not sure if anyone else has pointed this out yet but with sylveon, there are now 9 eevee/evolutions and 18 types of pokemon with the addition of fairy type.

Now we also have mega evolutions and that made me wonder. What if each eevee/evolution had a mega evolution? Not only that, but what if the mega evolution forms gave them the other 9 missing types in the eevee line?

We already know with ampharos that typing can be affected by the mega evolutions. Also, I know that not all pokemon will have a mega evolution, but eevee IS the evolution pokemon and it just makes sense they would have a mega evolution.

Some examples
Eeevee becomes Fighting type
Umbreon becomes Poison
Espeon, becomes Ghost
Leafeon becomes Bug
Glaceon becomes Steel