West
This is the direction to watch, and in many way makes the most sense in the short term.
Should the SEC look beyond Texas, where it has the Dallas (5) and Houston (8) secure, the next major markets in that direction geographically are Phoenix (11) and Denver (16), which translates to Arizona State and Colorado. It would also open the door to California.
Consider this option for the SEC: Adding four teams from the Pac-12.
Phoenix to Seattle, which has been a common trip for years in the Pac-12, is roughly 1,100 miles in the air, and 1,400 miles driving.
Phoenix to Birmingham is 1,400 miles, just with more time-zone changes.