If the Big Sky nabs any of the Dakota schools, Cal Poly and UC Davis BETTER change their minds unless if they want to be football independents, or play football in the Big South, and possibly for a very long time. The only downside is there won't be room for everyone in the Big Sky, unless if some schools move up to I-A, or if enough schools move down from I-A to form another full-sized I-AA conference out west.
I think what you will hear from Cal-Davis or Cal Poly people is that they don't want to give up the Big West for their other sports for the Big Sky. They would rather stay independent than have to commit to another all-sports conference other than the Big West. They would prefer having the Great West Football Conference stay together, but if not, independence I believe is what they prefer to all-sports to the Big Sky, sacrifice the Big West thing.
I think a forum site where the Cal Poly's and Cal-Davis' fans hang out is www.anygivensaturday.com
IIRC where I think they reflect on this perspective.
Cal Poly made it into the I-AA playoffs last year from the GWFC, and yet did so without the GWFC being an automatic qualifier to the playoffs IIRC. Cal Poly was an at-large pick. If they can maintain scheduling with SUU and amongst themselves as well as Big Sky members and Big South members and the Dakota schools, and keep their schedule strength up, they may not need to be in a conference for football.