Unfortunately I'm not too familiar with the Pac-12 situation. Maybe someone can help us out?
I'm quite sure that a conference with Berkeley will be very much against adding a school like BYU. If any place it would be Big XII.
Boise State is interesting because they are a Pac-12 member in Wrestling. They would probably be last resort.
Per my understanding, they still would consider going to 16 with parts of the Big XII (Texass, OU/Okie Lite combo) and decent schools not in their current footprint (read: Nevada). Scott, while amicable with Texass, wasn't exactly happy with what went down and how it happened, and he may be gunshy about going after Texass again. Boise State is on their radar, but just barely, and frankly, they would probably need to show sustained success and growth for them to be considered.
And you're correct about BYU. The California schools are steadfastly opposed to BYU...which is why Utah got the nod over them. And the Pac-12 wouldn't dilute the earnings by bringing in a school in the same state as Utah with (limited) national appeal. And yes, BYU brings in decent numbers via their religion, but they have a hard time bringing in anyone else.
As for the conferences, I could honestly see the Big XII being scattered to the wind before the ACC. Whatever the Pac-12, SEC, and B1G don't pick up will be assimilated by the remnants of the ACC or the Mountain West, the latter of which is possibly flirting with a seat at the big boy table.
I could also see a Big XII marching on with schools like Houston, Tulsa, Colorado State, New Mexico, etc. and becoming Conference USA v2.0.