Here's what I would do (if anyone cared what I would do) and I think it's realistic, maybe until the last point.
1) Add BYU and Houston.
2) Create the following divisions:
Big 12 East
Baylor
Houston
Iowa State
Kansas
Kansas State
West Virginia
Big 12 West
BYU
Oklahoma
Oklahoma State
TCU
Texas
Texas Tech
3) Set up an 8-game conference football schedule (own division + half of other division, like the original Big 12, with no protected rivalries) with minimum 2 Power Five opponents in the non-con.
4) Retain the 18-game conference basketball schedule, playing own division home/away (10 games), 1 protected crossover home/away (2 games), 1 of the remaining 5 (rotating) in the opposite division home/away (2 games), and the remaining 4 teams once, either home or away.
Protected basketball crossovers would be:
Baylor & TCU
Houston & Texas Tech
Iowa State & Oklahoma State
Kansas & Texas
Kansas State & BYU
West Virginia & Oklahoma
5) Play the Big 12 championship game at Jerryworld in Dallas and extend the Big 12 basketball tournament at the Sprint Center for a long, long time.
6) Extend the GOR also for a long, long time.
7) Begin exploring the possibility of working with ESPN to repurpose the Longhorn Network into a Big 12 Network.