This sucks, I run hashcat with wordlists a lot locally on my mac before sending it to our dedicated crackingstation at work. Would be a shame if this would no longer be possible.
I read on
https://en.wikipedia.org/wiki/Metal_(API) that "Metal combines functions similar to OpenGL and OpenCL under one API.", hopefully it won't be a big leap to make hashcat work with Metal.
Speculation: likelihood of adopting a separate platform is probably low. Unless someone comes up with a "MetalCL" shim / abstraction layer, this may mean dropping Mac as a supported platform.