Cook bacon in a large Dutch oven over medium, stirring occasionally, until crispy, 10 to 12 minutes. Using a slotted spoon, transfer bacon to a paper towel-lined plate, reserving 2 tablespoons drippings in pot; discard remaining drippings or save for another use.
Add sausage to pot, and cook over medium, stirring occasionally and breaking up with a wooden spoon, until browned, 5 to 7 minutes. Transfer sausage to a medium bowl using a slotted spoon, reserving drippings in pan; set aside.
Add onion, fennel, garlic, fennel seeds, black pepper, and red pepper to reserved drippings; cook over medium, stirring often, until softened, 6 to 8 minutes.
Stir in broth, water, potato, cheese rinds, and salt, scraping up browned bits on bottom of pan. Bring to a boil over medium-high. Reduce heat to medium-low; simmer, covered and undisturbed, until potatoes are almost tender, 4 to 6 minutes.
Stir in kale and reserved cooked sausage. Bring to a simmer, uncovered, over medium; cook, stirring occasionally, until kale is wilted and tender, 3 to 5 minutes.
Remove from heat, and stir in cream and vinegar; remove and discard cheese rinds.
Divide soup evenly among 6 bowls; sprinkle with reserved cooked bacon, and garnish with black pepper, crushed red pepper, grated cheese, and olive oil.
