Since we're spit balling, I think its time to really shake things up and make the Republicans deal with a curve ball. To that end, I'm throwing Andy Beshear, Governor of Kentucky (a southerner) and Gretchen Whitmer, Governor of Michigan (a mid-westerner) on the wall.
Beshear is down to earth, super smart and respected by even the most strident conservatives (proven by re-election last November). Whitmer is mid-west clean through, smart as a whip, and electable.
Neither one of them are coastal elites, or Washington insiders. They are straight-shooting, straight-talking Americans. Put one or both those people on the Democratic ticket and rural, southern and suburban voters would finally see a real alternative to Trump.