Reports coming out of Japan quotes Gayu Eusegi, head of Mitsubishi's global product development as saying that the Lancer Evolution X will be the last Evolution. According to the reports, Eusegi says that it's part of a shift towards leadership in Electric Vehicle (EV) technology.
In the same report, Eusegi killed any notion of a high-performance hybrid, unless, "The world can change, and...we can do a motor race by electric vehicles. Maybe then we can enter the market again."
In a related report, magazine Autocar says that Mitsubishi will release eight fully electric or hybrid-electric vehicles by 2015 and that the Evolution doesn't fit that mindset.