While it is not impossible to imagine a moderate, New Democrat from the South winning the nomination in this day and age, it would be a very unlikely feat. There are three big reasons.
The first is that the breeding ground for this kind of moderate Democrat really is the South and the Border States, which historically were the conservative “ballast” against the Northern, liberal factions in the Democratic party. However, in the last 30 to 40 years, these areas have trended decisively to the Republican party. That simply reduces the number of potential candidates (governors and senators) who could contest the nomination from such a centrist position.
The second is that as Southern whites have moved into the GOP, the ideological character of the Southern Democratic party has shifted. African Americans now dominate the primaries in the South – as was evidenced by Obama’s rout of Clinton in the region – and they have long aligned themselves more closely to the Northern, liberal factions of the party. That presents an added challenge for a moderate Southern Democrat, as he could be beat from the left by a Northerner.
Third, Super Tuesday has lost its Southern flavor. In 1992, six of the eight primaries were from the South — yet in 2008 just six of the fifteen were. It’s hard to imagine Bill Clinton coming out of Super Tuesday as the frontrunner if California, Connecticut, Massachusetts, and New York had all voted that day in 1992.