1. Process first 3 ingredients and 1/4 tsp. salt in a blender until smooth, stopping to scrape down sides.
2. Transfer avocado mixture to a bowl; stir in buttermilk, 3 Tbsp. lemon juice, and, if desired, wine until smooth. Place plastic wrap directly on soup, and chill at least 1 hour or up to 4 hours.
3. During last 15 minutes of chill time for avocado mixture, combine shrimp, olive oil, lemon zest, and remaining 1 Tbsp. lemon juice and 3/4 tsp. salt, and let stand 15 minutes.
4. Ladle soup into small bowls, and top each with shrimp. Garnish, if desired.