When I do 2-hr sessions, I only book them with providers I know who give excellent TS, have excellent TM skills, have great personality for conversation, and can unleash skills and patience for extended edging, multiple shots and serious ball draining.
For 3-hr I would push into previously unexplored/under-explored areas. Toys would be a good area. It would have to be something really special because 3-hrs is a really long time. You could schedule breaks for hydration, a snack, a bathroom break, a nap...