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Found this courtesy of Cooks Illustrated/America's Test Kitchen:

Coleslaw with Bacon and Buttermilk Dressing
Published: September 1, 1999
Makes scant 5 cups, serving 4 to 6

Salting and draining the onion with the cabbage helps mellow harsh raw onion flavors.
INGREDIENTS

1 pound green cabbage (about 1/2 medium head), shredded fine
1 large carrot , peeled and grated
1/2 medium onion , sliced thin
1 teaspoon table salt
6 slices bacon (about 6 ounces), cut into 1/4-inch pieces
1/2 cup buttermilk
2 tablespoons vegetable oil
2 tablespoons cider vinegar
1 tablespoon caraway seeds
1/4 teaspoon dry mustard
2 teaspoons granulated sugar
Table salt and ground black pepper

1. Toss shredded cabbage, carrot, and onion, and 1 teaspoon salt in colander or large mesh strainer set over medium bowl. Let stand until cabbage wilts, at least 1 hour or up to 4 hours. Rinse under cold running water (or in large bowl of ice water if serving immediately). Press, but do not squeeze, to drain; pat dry with paper towels. (Can be stored in zipper-lock bag and refrigerated overnight.)
2. Fry bacon in medium skillet over medium heat until crisp and brown, about 6 minutes. Transfer bacon with slotted spoon to plate lined with paper towels; discard fat.
3. Stir together buttermilk, oil, vinegar, caraway, mustard, and sugar in medium bowl. Toss cabbage, carrot, onion, and bacon in dressing. Season to taste with salt and pepper; cover and refrigerate until ready to serve.

Creme fraiche or the greek yogurt ride&cook suggested work great.

This may sound gross - but I had some leftover Blue Cheese/Cream Cheese/Shallot/Garlic mixture left over (had been used to pipe into Endive). I shook the hell out of it in a jar with Buttermilk and it came out fairly close to a Mayo/Buttermilk dressing. Cream Cheese may be worth experimenting with in leiu of Mayo with Buttermilk.