The Big 12 does not have 12 teams now, and it will not have 12 teams in the future unless it starts adding to its arsenal. The number 12 at this moment is a reference to the invisible 12th planet in our solar system, I think. The Louisville Cardinals and BYU Cougars remain the presumed top candidates for those two spots, with fresh rumors regarding the status of the boys from Provo.
BYU's Rivals site reports the Cougars are "aggressively pursuing" membership in the Big 12, which follows previous reports that BYU's particular stances on certain media issues would prevent such a partnership. According to Deep Shades of Blue, both BYU and Louisville could be added in time for 2013. BYU would join in all sports, according to the report.
BYU is currently independent in football, and Louisville remains one of the Big East's football crown jewels for the time being.
For more on Cougars football, visit BYU blog Vanquish The Foe.