We're talking 2200 miles and adding a Pacific Time school.
Realistically, I don't even think the Big 12 goes for BYU (given that they have strong options that are better geographic fits in UCF, Cincy, Houston, Memphis), but UNLV is definitely not happening.
Of course, that's all based on the idea that West Virginia is in the conference. If the ACC poaches West Virginia, then suddenly westward expansion opens up again. At that point it's deciding between UCF/Cincy/Memphis and BYU/Boise/UNLV, but Houston could fit with either