So UE 4.11 is now out with Metal for Mac out of beta and the default renderer as promised.
Interestingly there's a note about a commandline to activate experimental SM5 features. I wonder what that adds? Additional features already available in Metal that don't fit the union of OpenGL 4.1 and Metal featureset (since right now the OGL4.1 and Metal renderers offer feature parity) or is this access to new features beyond what Metal officially supports such as tessellation?
"Shader Model 5" is Microsoft's name for the feature-set defined by Direct3D 11. In UE4 enabling Metal's experimental Shader Model 5 support means using Compute shaders for various post-process effects and allowing texture-cube-arrays, obviously we can't support things like tessellation that Metal itself doesn't actually provide.