I leave in all the current members for now. And I go for 4 new members: Arkansas, Colorado State, SMU, and TCU. They all have sports they are good at, and the latter 2 are also added to strengthen the hold on the Dallas-Fort Worth TV market. SMU and TCU also join because of their proximity to Big 12 HQ. UArk and CSU go in the North Division, and SMU and TCU in the South. Division play is then started for other sports.
UT and A&M have a ton of grads in the DFW area. I don't really know how much TCU and SMU add to that. Arkansas almost cetainly would not leave the 12th share of SEC $ for a 16th share of the same (smaller than the SEC) TV footprint the Big XII already has.
Now the idea of dumping Baylor and adding CSU is absolutely something Nebraska should be pushing for. That effectively would kill the MWC, reducing it to near WAC levels and might prolong the existance of the Big XII.
Without CSU, it is very difficult for the MWC to claim relevance in Denver, even though Wyoming is technically in that market and Air Force is in the neighboring Colorado Springs Market. That forces the MWC down the mountain network path irrevocably as their cottage cheese footprint would look quite spotty from a media perspective. They have a good hold on SLC, San Diego, Las Vegas, and Albequeque, but that is only about 3M TV housholds owned and fingerholds in Colorado and DFW. If CSU (one of the MWC's 3 other tier 2 or better schools) left, I could see TCU dropping out. I think they would do better in a 14 team CUSA or frankly as an Indy with their own small TV deal.
Then if Missouri and Iowa State go to the Big Ten, I go after LSU and Tulane to add the New Orleans market. The Oklahoma schools go to the North Division to make room for the Louisiana schools in the South.
I can't see the Big 10 going to 13, and I doubt Iowa State is on their radar (as much as I wish it was). Good academic school, good athletics, no added market. Missou is a very sensible Big 10 add, but is probably no higher than 4th on their list of options behind ND, UT (pipe dream), and rutgers.