Although Baylor is still, for the moment, holding up the official announcement of Texas A&M joining the SEC as its 13th member, it's extremely likely that the Aggies will be joining the SEC in 2012.
The Aggies would most certainly be placed in the SEC West alongside Arkansas, Mississippi State, Ole Miss, LSU, Alabama and Auburn. That would make for an unbalanced division, however, with six teams currently in the SEC East. Although the Big 10 made it work with 11 after adding Penn State, having an odd number of teams in a conference, let alone a single division within a conference, presents scheduling challenges—not to mention challenges in parity and the number of teams as it relates to getting to the SEC championship game.
It seems likely, then, the SEC would seek to add a 14th team...perhaps even adding three teams ultimately, which would make 16 and potentially match what's about to occur with the Pac-12 and the break up of the Big 12.
So, which team is the most likely addition beyond A&M?
The Tigers are an interesting proposition for the SEC. First, the ability to bring the St. Louis television market and stronger recruiting ties to middle America to the SEC adds value, as does Missouri's strong academics. On the field, Missouri's been a well-above par performer in the Big 12 and head coach Gary Pinkel's squad finished 10-3 last year and are currently ranked 21st in the AP poll.
Second, Missouri (the state) shares a border with Tennessee, Kentucky and Arkansas and is geographically well-positioned for fans and teams to travel. Also, Missouri plays at Memorial Stadium with a capacity near 69,000.
If Missouri does ultimately join the SEC, I think you'd see some minor realignment of the divisions to better account for geography while trying to hold on to some traditional match-ups.
I could see Kansas, Kansas State and Iowa State jumping to the Big Ten with Oklahoma, Oklahoma State, Texas and Texas Tech bolting to the Pac-12. That leaves Baylor without a seat when the music stops. As a large private school in the middle of nowhere, who only recently has begun to earn some measure of respect on the football field, it doesn't seem likely Baylor would be a candidate for SEC inclusion. The only reason in taking a look at Baylor from a SEC perspective would be for academics— a la Vanderbilt. But almost every conference already has a Vanderbilt, or Northwestern, or Duke, or Stanford. Baylor doesn't add anything to the SEC that the SEC wants or needs.