Staying in the Southeastern United States, the next conference I will look at is the Big South Conference. Right now it has 12 members--4 in each of the states of Virginia, North Carolina, and South Carolina for a neat geographic footprint. The Big South plays FCS football. Its members are:
Virginia Military Institute
Schools in Blue are private.
* Non-Football school
Stable for now, this league's football schools will soon be courting the SoCon if they haven't started already. It's hard to say who the leading candidates would be. Coastal Carolina has a solid program that would fit with the SoCon's geography. Liberty is also strong but they are further north and they are evangelical which might be a turn-off for some of the SoCon's members. Gardner-Webb, while not having an exceptional program, is similar in profile to the private schools in the SoCon.
As far as schools potentially entering the Big South I think the schools in the Atlantic Sun who field are or planning to field football teams are the most likely.