Cook the bacon in a skillet over medium heat, turning, until crisp. Transfer to paper towels to drain and reserve 1 tablespoon of the drippings. Chop the bacon.
Preheat the oven to 400 degrees F. Rub the potatoes with the olive oil and season with salt and pepper. Place on a baking sheet and bake 30 minutes. Pierce each potato in a few spots with a fork and continue baking until tender, 15 to 20 more minutes.
Meanwhile, fit a medium pot with a steamer insert, fill with 2 inches of water and bring to a boil. Add the cauliflower, cover and steam until crisp-tender, about 10 minutes. Transfer the cauliflower to a food processor. Add the buttermilk, garlic, vinegar, paprika, the reserved bacon drippings, 1/2 teaspoon salt, and pepper to taste; pulse until smooth. Set aside 1/4 cup of the cauliflower puree for topping.
Slice a thin layer off the top of each potato, then scoop the flesh into a bowl, leaving a 1/4-inch-thick wall. Mix the potato flesh with the remaining cauliflower puree, three-quarters each of the cheese and scallions, 1/2 teaspoon salt, and pepper to taste. Stuff the potato skins with the potato-cauliflower mixture and sprinkle with the remaining cheese. Bake until the cheese melts and the filling is warmed through, about 12 minutes. Top with the reserved cauliflower puree, the remaining scallions, the bacon and more paprika.