Cramming more gears into an automatic housing rarely makes the transmission stronger. AMG stuck to the old 5-speed automatic for quite some time in AMG cars due to the torque they generate. Only recently have they switched to the 7G in the big torque 65 AMG models and it is doubtful the 9G is up to the task of 738 pound-feet of torque.
The 9G transmission improves fuel economy figures by 2 miles per gallon on the highway in the E350 BlueTec. City figures improve by a surprising 3 miles per gallon. 0-60 remains 6.6 seconds.
Will transmissions stop here or add more even more speeds? Considering 7-speeds have now become routine and the same will likely happen with eight and nine speeds one should not bet against it.