I have not officially begun to test / port the MU-2 to X-Plane 12; HOWEVER,  I have been testing it regularly in X-Plane 12 and the good news is that it seems at first glance....to be mostly functional....FOR.....daytime flight.  I say this because the biggest change in X-Plane 12 is the new atmospheric and lighting engine..and this requires new "directive commands" for lighting that were not present in X-Plane 11.  The nightlighting is practically non-existent until I make the required changes.