I've heard a hundred different scenarios: Texas goes independent, Mizzou and Nebraska goes to the Big 10, and my personal favorite...the BIG 12 south joins the Pac 10 to form a super-conference.
If the south does join the Pac 10...well that would just be crazy.
Think about Texas, Oklahoma, Texas Tech, Oklahoma State, USC, Oregon, Cal, Oregon State, Stanford, UCLA. Definitely enough to rival/surpass the SEC.
Personally, I doubt anything that drastic happens.