In fact adding BYU impacts their problems. First issue is that they need another top tier program that isn't OU and Texas... A&M and Nebraska used to be in that group... they are gone. Nebraska isn't happy in the B1G... maybe the BIGXII can convince them to come back, that would actually be a very big gain for the conference.
The other issue is West Virginia... adding TCU made virtually no sense at all, but adding West Virginia in comparison did absolutely nothing for the conference... it's not given the conference any leg up on the East coast at all... it's created a head ache for travel, as would BYU BTW. When Louisville was there for the taking and they skipped past Louisville and went for UWV... it's clear that the BIGXII decision makers have extremely low IQ's.
Adding BYU and Boise State makes absolutely zero sense... adding Boise is just adding another West Virginia. Colorado State doesn't bring anything that the conference lost with Colorado. BYU would have to come with Nebraska and/or Colorado coming back and West Virginia leaving the conference. And I just don't think we see any of that happening.
BYU isn't going to the BIGXII any time soon.