Here is an interesting article on the P5 college team TV viewers. The analysis is for 2015 – 2019.
Which college football programs bring in the most TV viewers?
ISU and TCU are specifically mentioned in the article. The TV rankings of the P5 programs along with the teams that could be added to the Big 12 are included. It's a
little disappointing to see ISU ranked at #44. OSU (#19), TCU (#24), Baylor (#35), and TX Tech (#37) are ranked higher than ISU. Those teams probably benefit from the Texas market. It will be interesting to see what happens without TX and OU. West Virginia (#30) is also ranked higher than ISU. They would be a good fit in the ACC. Kansas State is at #51 while Kansas is very close to the bottom of the list at #70).
Possible B12 additions include BYU (#46), Houston (#50), UCF (#58), Memphis (#59), Boise State (#62), Cincinnati (#64), USF (#66), and SMU (#73 - last on list). Iowa land Nebraska look good at #21 and #22, respectively. Former Big 12 Colorado is about where you would expect at #56. It is surprising that Missouri is ranked at #55. Rutgers is at #72 which is discouraging to see on behalf of ISU which fits the Big 10 better.