What are the biggest energy-efficiency trends for pools right now?

Variable-speed pumps and heat pumps. A variable-speed pump cuts electricity bills by 50–80% compared to a single-speed pump, with payback under two years. For heating, a heat pump uses less energy than a gas heater and pays for itself if you heat your pool for more than a couple months a year. Start with the variable-speed pump, then the heat pump if you need heat.