And because we had too many of Gen 2 pokemon implemented, it was another reason why we didn't get Johto, so adding the pokemon Spiritomb should be a no go. I wouldn't want Sinnoh to become another Johto.
Besides, we have Choice Scarf Mismagius, Choice Specs Mismagius. Hell we can even have Specially Defensive Cofagrigus with Calm Mind and leftovers. And you're telling me that these pokemon without nasty plot is useless? C'mon son.