They started working on Metal before they knew AMD will give Mantle to Khronos to make Vulkan. So the open question is, whether Apple will support Vulkan or will sabotage it in order to preserve lock-in.
Unlike MS, Apple participates in Khronos Vulkan group if I'm not mistaken. Even Sony does. No idea about Nintendo.
Being part of Kronos doesn't mean they are forced to implement any of their standards.
Sony is a good example. The only Khronos stuff they use is WebGL in the PS4 menu and that OpenGL ES 1.0 with Cg shaders for the PS3 that no one used. All studios targeting PS3 favoured LibCGM (http://sandstormgames.ca/blog/tag/libgcm/).
No idea what they actually do, but if they'd add Vulkan support to PlayStation, it would be good for developers. Some Apple developers so far participated in SPIR-V / LLVM related discussions. And MS was notably absent in anything related.
As I said, when they'll fix this lock-in mentality, I'll second the claim that they seriously changed for the better.
Vulkan is still an abstraction. Most PS4 developers I know would prefer the stuff they already have which is closer to the metal. Something that uses the actual instructions for the PS4 GPU and not some cross platform API that then has to be translated to the actual GPU.
Yes, PS4 devs porting to PC would likely like Vulkan over OpenGL or DirectX but PS4 devs on PS4 not so much.
Making games for only one platform doesn't make sense since it limits reach, and using tons of incompatible APIs is annoying as well. Vulkan is low enough of an abstraction to perform quite well, so no matter what direction something can be ported, having a common API can save a lot of time.
Unlike MS, Apple participates in Khronos Vulkan group if I'm not mistaken. Even Sony does. No idea about Nintendo.