I know Metal was announced for iOS earlier - I was talking about the support for Mac OS X. They had no good reason to adopt it for Mac OS X at that point, if they were planning on adopting Vulkan in the near future anyway. Unless, like I said, they'd prefer to keep Metal over Vulkan, and wanted to give it a head start to see if PC game developers would start adopting it.
> If that was the plan, it's probably going to fail: The developers of Unity e.g. found Metal, DX12 and Vulkan so similar that they estimate to be able to support all three with minimal development overhead.
I'm not sure how you see that as a "failure". If they are so similar that game engine developers will keep Metal around anyway, then we'll see games be built on Metal, not Vulkan, for Mac OS X. How is that a "failure"? It would mean Metal "won".