I remember seeing something like this on a proof of concept demonstrator at Paris or Farnborough back around '87 or '88. At that time GE called the concept UDF for unducted fan. One UDF engine was mounted on an MD-80 series airplane while the other side carried the standard JT8D-200 series fanjet. It was billed as being able to provide massive fuel savings to cost conscious airlines. But what was remembered by crowds witnessing the flight demo was the cacophony of ear-splitting noise emanating from the beast. Between that, concerns expressed over the structural integrity and damage tolerance of the blades and the development of higher bypass and more efficient fanjets, the project never really went anywhere. The idea still has it's supporters to this day though, so it resurfaces from time to time.
Edit: I found an interesting historical perspective on the project
here. Enjoy!