Could the entire south be in play? Holy crap.
Of course -- if white Southerners are going back to the partisan patterns normal when Jimmy Carter was President, Hillary Clinton could be on the way to a 450-EV win in November. But if only as they were in the 1990s? We could see her pick up every state that Bill Clinton ever won in the 1990s except perhaps Montana -- but win Virginia.
Carter 1976, Obama 2008/2012
Carter 1976, Obama twice red
Carter 1976, Obama once pink
Carter 1976, Obama never yellow
Ford 1976, Obama twice white
Ford 1976, Obama once light blue
Ford 1976, Obama never blue
Let the Republicans have everything in blue, and only everything in blue (maybe exchanging Alabama for Arizona), and the Republicans have a nightmare -- their worst election since at least 1964 for the Presidency.
I'm not saying that this happens.
This map is even messier, if only less decisive a Democratic Presidential win:
deep blue -- all elections for the Republican
medium blue -- all but one election for the Republican (but once for Obama)
pale blue -- all but once for the Republicans (but once for Clinton)
deep green -- Clinton twice, but Obama losing by more than 10% twice
medium green -- Clinton twice, Obama barely losing once
yellow -- Clinton once, Obama twice
tan -- Clinton never, Obama twice
medium red -- all but one election for the Democrat
deep red -- all elections for the Democrat
white -- always went for the winner (Clinton twice, George W. Bush twice, Obama)
...imagine anything not in dark blue, and the Republican nominee still faces the worst landslide loss for a Republican since 1964.