I wouldn't see any reason for the Big Sky to go 12-it would also make more sense for Cal Poly SLO and UC Davis to play Big Sky football rather than the four Dakota schools. I also think Sacramento State and/or UC Davis would upgrade their football programs and join the WAC; even if both of those came to pass, the Big Sky would still have at least six for football. The Big Sky could add Denver and Utah Valley State if more members are needed for all sports. Even San Diego may move to scholarship football.
Also, if all four Dakota schools are in The Summit (formerly the Mid-Continent Conference), along with Southern Utah and Western Illinois, that makes six for football-those schools will probably be required to play Summit League football.
MWC Pacific: Boise State, Fresno State, Sand Diego State, UNLV, BYU, Utah
MWC East: Colorado State, TCU, Air Force, New Mexico, Wyoming, UTEP
WAC (10): Hawaii, SJ State, Nevada, Sacramento State, California-Davis, Idaho, Utah State, New Mexico State, Portland State, Montana
Big Sky (9): Idaho State, Eastern Washington, Northern Arizona, Weber State, Montana State, Northern Colorado, Cal Poly SLO, Denver, Utah Valley State