According to a source talking to Jimmy Hyams of Knoxville sports radio station 990 AM the Sports Animal, Mike Slive has met with CBS to discuss possibilities regarding SEC expansion. Supposedly it would only happen if the Big Ten goes to 16, and the targets would be (predictably) Texas, Texas A&M, FSU, and Clemson. Should the Texas schools decline, the next choices would be Miami and Georgia Tech.
The SEC issued a swift denial, so caveat emptor and all that. At the very least this one sounds plausible because Plan A would add two teams to each division and we don't have to worry about schools leaving their current divisions.
I will say this though: you couldn't find a worse cultural fit for the SEC in the region than Miami. If you already think that Florida seems sort of like an outsider, Miami would feel like something from another planet.