Place the bacon on a sheet pan fitted with a wire rack. Roast the bacon until crispy, about 20 minutes.
Pour the bacon fat from the sheet pan into a large skillet and warm over medium-high heat. Add the onions to the skillet and cook, stirring frequently, for about 1 minute, then sprinkle in the garlic powder, ground mustard, pepper and 1/2 teaspoon salt. Reduce the heat to medium-low and continue to cook, stirring occasionally, until the onions are browned, soft and caramelized, 30 to 45 minutes. Set aside.
Preheat the broiler.
Stir together the cream cheese, yogurt, mayonnaise, parsley, Worcestershire, 1/2 cup Cheddar, 1/2 cup Swiss and the remaining 1/2 teaspoon salt until completely combined. Stir in the warm onions.
Cut the top of the boule off and hollow out the center. Place the boule on a parchment-lined baking sheet. Save the scooped out chunks of bread and cut the removed top into pieces to dip later.
Fill the boule with the onion mixture and sprinkle the top with the remaining cheeses, holding back a tablespoon of each. Cut the bacon into 2-inch pieces and arrange them like the rays of the sun around the perimeter of the dip, then sprinkle the remaining cheese in the middle, overlapping the bacon to make an extra-cheesy center. Broil, watching closely to prevent burning, until the bacon is crisp and the cheese is melted beneath, about 2 minutes. Serve warm with crudites and reserved chunks of bread and use the bread bowl/bacon for dipping!