Yeah forget metal. Apple should focus more on supporting opengl. DirectX and GL are already fantastic graphical APIs.
Everything I've heard says that Vulkan and Metal both are far more efficient, let you get more out of the hardware with less CPU time, and can more easily support newer features.
OpenGL as a major target platform is dying, it's just a question of how long the tail is.
Even from the perspective of bringing people smoothly to their proprietary API, they have failed miserably.