Two things:
1) the Pac 12 will never be forced to add any teams it doesnt want. Period. If there are no candidates worth targeting, the conference will stay at 12 forever.
2) if by some miracle they were forced to add, you seriously think the Pac 12 would go for BYU over Oklahoma, Okie State, Kansas, K State and Baylor?
BYU will never get into the Pac 12.