Cover beans with water by 2 inches in a pot and bring to a boil. Remove from heat and let stand, uncovered, 1 hour. Drain beans in a colander and rinse. Cook onions in oil in an 8-quart pot over moderately low heat, stirring occasionally, until softened, 4 to 5 minutes. Add garlic and cook, stirring, 1 minute. Add beans, broth, 1 quart water, cheese rind, salt, pepper, bay leaf, and rosemary and simmer, uncovered, until beans are just tender, about 50 minutes. While soup is simmering, brown sausage (if using) in batches in a heavy skillet over moderate heat, turning, then transfer to paper towels to drain. Stir carrots into soup and simmer 5 minutes. Stir in kale, sausage, and remaining quart water and simmer, uncovered, stirring occasionally, until kale is tender, 12 to 15 minutes. Season soup with salt and pepper.