If say this happens, I dour it's a geographical split. Best guess would be an acc style split. Probably be something like this: group a, isu, ksu, okla, tex, tcu Memphis. Group b, wva, Ksu, ok state, baylor, tech, cinci. Nine game with one cross division rival played every year. So, in this case: isu vs wva, kan vs kstate, ou vs osu, tech vs tex, tcu vs Baylor and cinci vs Memphis.
Im sure u could flip flop some teams in there but something like this seems like a likely scenario. It help preserves rivalries while having two relatively equal divisions. A north south split is gonna cause a def haves vs have nots scenario which was one of the main causes of the original split that happened five years ago.
I also think an ACC-style split would be most likely if the Big 12 were ever to expand back to 12 teams. Two Texas schools per division and probably one Oklahoma school in each as well so everybody keeps that southern access for recruiting.