A lot of it depends on the order, but we're talking about 4 leagues (ACC, Big Ten, Pac 12, and SEC) adding 6-8 teams EACH.
ISU is included in this 18-20 structure for sure. In fact there would be competition for our inclusion because it would likely mean some leagues would be adding non BCS teams with inferior facilities. Which is why 18 would be more likely than 20. 16 involves law suits of kicking teams out of the BCS, 20 involves raising up a few teams with questionable facilities.
Let's say there's this push to 18-20 based around the 4 leagues that seem to not get poached, here's what could happen:
Pac 12 mostly gets over half it's expansion from Big 12, Most likely OU/OSU and some Texas schools, slim chance KU/KSU but likely not ISU/Missouri. They probably also pick up BSU/BYU and maybe Nevada. Academic tradition no longer exists if every league is 18-20. It's just football/revenue now. So the Pac 12 covers about 1/3 of the country now. Why would they prefer to get one or two new teams in the east or central time zone when they already cover 1/3 of the nation solid. Current Pac 12 commissioner was hyper aggressive last round and they are the most isolated geographically so I'm guessing they expand first, he's also the only one whose PUBLIC GOAL is 4 16 team leagues already.
Big Ten, ACC and SEC would be left. They each need to add 6-8 teams, 18-24 total. All they have to chose from is Notre Dame, 9 Big East teams, maybe 2-5 Big 12 teams, and non BCS schools.
The only way ISU WOULD NOT be in the Big Ten in that scenario is if the Big Ten went to 18-20 teams while everybody else sat still with 12 with the only goal being a larger television footprint. Any other scenario and ISU ends up grouped with the current Big Ten schools. ISU fits the Big Ten's current footprint better than any other team, we're exactly in the center of three existing teams and they probably added 4-5 "new market" teams already.
There simply aren't enough teams for 18-20 where we're not in the Big Ten, especially 20. Do people think being with the current ACC teams is more likely because that's the second most likely spot if the hypothetical 18-20 team leagues come about?
4 superconferences will shake out like this with 70 schools:
1) A&M & West Virginia are 13th and 14th SEC teams.
2) School Presidents are screaming, Government officials threaten intervention.
3) Commisioners, ESPN, Fox and CBS meet up to create plan to appease Presidents and Government.
4) ESPN will pay unreal money for 4 team playoff. 2 semi-final games on New Year's Day at rotating Bowl venues. Championship Game a week or so later at rotating Bowl venue prior to start of 2nd semester classes. Other bowls remain largely intact. 4 superconferences are formed with 70 teams total (current 67 BCS/AQ teams plus TCU, BYU and UCF). Conference championship games first Saturday in December prior to 1st Semester Finals. ESPN agrees to fund separate playoff system for C-USA, MWC, WAC, Sun Belt, MAC and service academies.
5) Presidents and key Government officials agree to plan contingent on all playoff pool money is distributed equally to all 70 teams.
Superconference dominoes fall as follows:
1) A&M and WVa to SEC
2) Top TV revenue producers ND and UT mull conference options and go separate ways. B12 and Big East dissolve.
3) In order to establish Southern recruiting presence and retain own 3rd Tier rights not available in B10, ND decides on ACC and brings with them UConn, Syracuse and Pitt.
4) UT takes OU, TTech and Okie State to P12. Larry Scott permits LHN to remain.
5)
Big 10 demands only AAU schools and picks up remaining AAU schools: ISU, KU, Mizzou and Rutgers.
6) Texas politics force TCU and Baylor to P12 with Texas.
7) Due to time zone issues, Larry Scott also agrees to take BYU and K-State.
8) SEC forced to pick up SE leftovers Louisville, Cincinnati, South Florida and Central Florida who agree to reduced SEC revenue shares.
New ACC
North: Maryland, Virginia, VA Tech, Boston College, Syracuse, UConn, Notre Dame, Pitt
South: North Carolina, NC State, Wake Forest, Duke, Clemson, GTech, FL State, Miami
New SEC
East: UCF, USF, Florida, Georgia, South Carolina, Kentucky, Tennessee, Vanderbilt, West Virginia
West: Auburn, Alabama, Miss St, Ole Miss, LSU, A&M, Arkansas, Cincinnati, Louisville
New B10:
East: Rutgers, Penn St, Ohio St, Michigan, Mich St, Purdue, Indiana, Northwestern
West: Wisconsin, Illinois, Minnesota, Iowa, Nebraska, Kansas, Mizzou, Iowa St
New Pac 20:
East: Texas, TX Tech, Oklahoma, OK State, Baylor, TCU, K-State, BYU, Utah, Colorado
West: Washington, Wash State, Oregon, Oregon St, Cal, Stanford, USC, UCLA, Arizona, Arizona St