Big 12 goes to 16 teams with a 8 game conference schedule.
Every team plays their designated rival yearly, and the 14 other teams rotate every other year.
Designated rivals are as follows
BYU/Boise St
Texas Tech/Oklahoma St
Kansas/Kansas St
Iowa St/Memphis
UCF/USF
TCU/SMU
Baylor/Houston
Cincy/West Virginia
Biggest issues are that
the Iowa St/Memphis 'rivalry' is a bit of a stretch
breaking up the Baylor/TCU rivalry is unfortunate
Luckily with an 8 game conference schedule, teams can choose to keep any other rivalry of their choice alive.
This would include (assuming OOC rivals are on baors with it) BYU/Utah, Texas Tech/Texas, Ok St/Okla, West Virginia/Pitt, Iowa St/Iowa and even TCU/Baylor by scheduling a supplemental game every other year.
Schools that don't have an OOC rival would just have an extra game to play with