As I said, just leave it out of the base game. Sims 1 didn't really have any supernatural stuff from the start.
Sims 2 had aliens, but it was terribly done. Where just green sims, nothing more. But still, sims 2 did offer a full base game experience and is probably one of the most improvements any videogame sequel ever had.
Sims 3 had a pretty lousy basegame too, and sims 4 has without a doubt been the worst base game in the series so I seriously hope they will learn their lesson and will lay a solid foundation for sims 5 that does not feel too empty.
