I'm thinking that the Pac-12 may look east for some AAC schools that have been trying to join power 5 conferences. Memphis seems like a obvious choice here. USF has been wanting a power 5 invite for a while (especially after UCF got into the Big XII), but that might be too far east for them. UTSA seems like a good choice and Tulane could be a good fit as well.

As far as the Mountain West, assuming none of their other members jump ship, the most obvious replacements would be New Mexico State and UTEP, although New Mexico will probably fight to keep New Mexico State out of the conference. C-USA is getting two new members next year in Delaware and Missouri State, so losing NMST and UTEP wouldn't be the biggest loss. Otherwise, the Mountain West would probably be looking at FCS schools who want to move up, which may include the Dakotas, Montana/Montana State, and/or Idaho (which used to be an FBS school).