I think that the good people of West Virginia would quibble over being reefed to as part of “the south”… though if their looking to rejoin the old dominion their more than welcome
At the same time I’d say that while the panhandle and the west of Florida is still very much a part of the south the urban east of the state has shifted it in a direction which means it no longer has so much in common with other southern states as it once did, States isn’t going to like that (!)
Overall I’d say that the Democrats’ local strength of support and organisation in Arkansas makes it the Southern state most likely to shift into the Democratic column. After Arkansas perhaps Louisiana which also has a strong Democratic state-wide organisation and then potentially Virginia which offers a solid base for the Democrats but would have to be won by appealing to rural voters, something Kerry simply couldn’t do in 2004.