I don't think the Big12 will want to stop at 14 schools. If USC, UCLA, Washington, Oregon, etc. decide to move on from the Pac12 and find a new home in the Big10 and/or SEC- then we could be headed toward 2 or 3 super conferences. If the Big12 is going to be one of those conferences, it would seem like more schools equates to more money. With linear networks, there is a limit to how much inventory a network wants to have rights to. But with streaming platforms, the limit isn't channel capacity, but maximizing revenue for the platform while maximizing revenue on a per/school basis.
IMO a bigger Big12 means more money for all Big12 members. I could see the following comprising a thriving Big12:
West: BYU, Utah, AZ, ASU, UNLV & SDSU (6 teams)
Mid America: ISU, KSU, KU, OSU, CU & TCU
South East: TT, Baylor, Houston, UCF, Cincy, WVU
That would position the Big12 should the ACC gets poached by the SEC/Big10 in the 2030's. Schools like Louisville, Pitt, Va Tech and Syracuse would seem like solid fits if the Big12 is the 3rd power conference.