I don't think it's really a breakthrough - Hall Effect Thrusters and similar ion propulsion have been around for a while. The Soviets used them in the 70's. Its

I don't think it's really a breakthrough - Hall Effect Thrusters and similar ion propulsion have been around for a while. The Soviets used them in the 70's. Its more the technology has reached a level of maturity and relability that it is now a good choice.