Baylor and TCU have been rivals for well over 100 years. Both private schools about 120 miles apart. It was the Baptists vs. what was at the time Texas CHRISTIAN University. Now it's sadly a secular college.
I'm not sure what other rivalries will develop with the New Big 12. Cincy and West Virginia makes sense geographically.
I hope BYU plays Utah yearly as it is a fantastic rivalry. BYU should eventually stomp them most years as your recruiting will improve tons and the PAC12 becomes weaker in football (one caveat: USC is going to be a top program every year with Lincoln Riley coming in. Great recruiter and QB coach).
Who do you think will be BYU's main rival in the Big 12? I certainly hope it is not Baylor since we are both Christ-centered schools and that just would not be right.
Can't wait for the new BIG 12! Wish it were tomorrow.