Facts about possible expansion candidates:
Memphis
City pop: 653,000, biggest city in TN, third-largest in the Southeastern US
Student pop: 22,000
Cincinnatti
Pop: 235,000
Student pop: 44,000
Central Florida
Pop: 240,000
Student pop: 61,000
South Florida
Pop: 346,000
Student pop: 48,000
BYU
Pop: 526,000
Student pop: 34,000
A little more information on UCF...
Located in Orlando, which is the number 18 media market in the US. As mentioned above, drew an average of 1.64 million viewers per game in 2013, which would be 40th highest in CFB and 6th highest in the conference (OU #16, OSU #19, UT #26, TTech #36, Baylor #37).
Football stadium opened in 2007 with capacity of 45K and averaged about 35K in 2012 (which is the most recent I could find quickly).