The planned new stadium in Columbia is supposed to help anchor the new Bull Street Development which is being planned and built on a 165 acre parcel that used to house an insane asylum.
This hardly guarantees that the Savannah Sand Gnats will move to Columbia, but it moves one step closer to Columbia building a stadium for a team. The Mets' contract with Savannah is up at the end of the 2014 season, as well. If the Gnats do indeed move to Columbia, it might not be as a Mets affiliate.
On the other hand, remember, not all rumors come to pass. The Binghamton Mets were supposedly on their way to Ottawa last November.