Don't look for a cooperative formation of 4 X 16 or 4 X 20 or 6 X 12 or any other neat and tidy arrangement. The two big guys aren't interested in that. If they were it could have been easily settled by now. They are motivated by different objectives and each of them wants to achieve such a superior position that allows for that side to impose their vision on the whole of college sports.
The SEC is following a plan devised by their exclusive media partner ESPN. ( I have been an SEC guy since my boyhood days in Alabama, but I think ESPN is the ruin of college football.) The SEC wants to assemble the most elite brands in football and MBB into single conference. They believe that TV ratings dominance will come to the conference who controls the most popular "national" brands. Names like Alabama, Georgia, Texas, LSU, and those usual suspects will get eyeballs in every part of the country even though they are located in one geographic region. They believe that this line-up will grow a revenue advantage over all other conferences, even The B1G, and that eventually they will be able to add Ohio State, Michigan, Notre Dame, Southern Cal, and whomever might earn them an increase in media revenue. Their vulnerability is in the possibility that The B1G might add schools in the Southeast, which invalidates the ESPN monopoly on TV ads in that region. The B1G already earns more media dollars than The SEC, and having a foot in the door in the Southeast would foul ESPN's plans.
The B1G seems to be interested in building a coalition (could we say "alliance"?) among the other conferences in hope of wresting control of college athletics from ESPN. They will be the leaders in exiting the NCAA and forming a new governing structure. Their intentions for growth have been directed toward Virginia and UNC, even since Jim Delany stole Maryland. What they really seem to want is Big Ten dagger in the heart of SEC/ESPN. Maybe two schools would be enough, and maybe just a loyal partnership with The ACC would be enough without any ACC movement. The B1G is very snobby about the academic status of candidate schools. AAU membership is desired, but I don't know if it would be an absolute necessity. I don't think the B1G wants to exclude The SEC. They want to exclude ESPN as a power broker and demote them back to media wonks.
I think the media contract between ESPN and The B1G will be interesting. Both parties face a huge downside if they don't get an agreement.