What would be the drawbacks of using a rotating engine as thrust reverser on airliners? What are the drawbacks for having engines mounted on an aircraft such that their direction can be hydraulically controlled for best performance and efficiency? The idea would be to turn the engine 180 degrees at landing so it can operate as a thrust reverser, even on jumbos like the Airbus A380 and the Boeing 747.  That would be some serious thrust reversing power.
I wouldn't worry to much about the mass of the engine. That's actually not the biggest problem. Instead, I'd be scared far more by the angular momentum. That turbine has a large moment of inertia and also a higher angular velocity.To flip it, you have to reverse the angular velocity. It's essentially flipping a gyroscope, but this is a gyroscope weighing several tons.