If the PAC expands there are two ways it COULD go
1. Stay west and go after BYU and UNLV. BYU has a great following and is a football school. Also BYU has a national following so even though the PAC had UTAH adding BYU could be a good add to the PAC. UNLV gives the PAC the Las Vegas Market and that comes with many benefits.
2. Try and get into the central time zone. This means that many combinations could happen but I see Texas Tech and Kansas. Texas Tech gets the PAC into Texas and Kansas fits the PAC mold. I think that OK St is somehow going to the BIG but if not you can put OK St in Kansas place.
I don't see your option one as a possibility. They already have a school in Utah, and their product is big in Nevada so they wouldn't gain much.
Getting into the central and eastern time zone may be important to them as they've been upset about times when their games have been played and are on--they want some 3:30 and 7:30 games.
Obviously they'd want to get into Texas because of the recruiting power there. ISU and KU they'd probably be fine with their academics. Oklahoma State brings a well financed athletic dept and a consistently good football program.
Don't know if they'll try to add all 8 which would probably not bode well for WVU if they expand, but I'd say that would be option 2 before adding BYU or UNLV.
Geographically they can go with Kansas schools, OK State and stay in contiguous states. After that then obviously Texas schools would also be in their footprint if they chose that direction.