Peel and section oranges over a bowl; squeeze the membranes to extract juice. Discard membranes. Reserve 1/4 cup of juice for sauce; place orange sections in a medium bowl. Cover and chill in separate containers.
Sprinkle pistachios into an 8-inch circle on a baking sheet coated with cooking spray.
Place 1/2 cup of sugar and 1/3 cup of water in a small, heavy saucepan over medium-high heat; cook until sugar dissolves, stirring frequently (about 2 minutes). Cook until golden, without stirring (about 5 minutes).
Pour caramel over pistachios; cool completely. Break brittle into large pieces; place in an airtight container. Add 1 cup water to pan; bring to a boil. Cook until any remaining caramel in pan dissolves; discard. Wipe pan clean with paper towels.
Place remaining 2 tablespoons sugar and 2 tablespoons water in pan over medium-high heat; cook until sugar dissolves, stirring frequently (about 1 minute). Cook until golden, without stirring (about 3 minutes). Remove from heat; carefully add 1/4 cup reserved orange juice, stirring until sugar dissolves. Return pan to heat, and cook just until caramel dissolves, stirring frequently.
Combine orange juice mixture, orange sections, dates, and cranberries. Serve over ice cream; top with brittle.