Not sure about the veracity of that report, but let's roll with it. Let's assume the GOR gets extended and BYU and Houston join the conference. I would be curious about how the divisions would shake out with 5 of the 12 schools in Texas.
I would imagine that every school would want a piece of Texas for recruiting purposes - like how the Pac-12 divvied up the state of California. So I'd think a West/East split might be more likely than a North/South.
Here's my shot at divisions that try to maintain rivalries intra-division so they can avoid an annual crossover rivalry. If the conference does go to 12, I'd love for the Big 12 to consider an 8 game conference schedule with a requirement that its members each play two Power 5 teams in non-con, but that's another topic. (Before you say "The networks want 9 games," no, they want inventory they can control, and more non-con games would mean an equal number of games under network control, but with more of a chance to make them interesting - i.e. ESPN getting West Virginia playing Pitt, or FS1 putting Iowa State against Arkansas at Arrowhead in KC.) 8 conference games is easier without the crossover rivalry - you'd just revert to the old Big 12 method of scheduling.
Anyway, I think this is the one of the only ways you could swing it. There are many more options with crossover rivalries.
Big 12 East
Baylor
Houston
Kansas
Kansas State
TCU
West Virginia
Big 12 West
BYU
Iowa State
Oklahoma
Oklahoma State
Texas
Texas Tech