Vulkan on the PC is really going nowhere fast (this long since release and I think only four or five things support it, with nothing exclusively), so I would assumedly the real benefits of this are more likely to be felt by cross-platform developers currently working with OpenGL code on macOS and wanting to move to something of higher performance without taking on the burden of supporting Vulkan/DX12 on PC and Metal on Mac.
Given the frequent and drastic improvements Apple have been making to Metal in terms of fixing driver bugs of late, I would be surprised if it ran on anything below High Sierra (we should be beta testing 10.14 by the time the game releases). Like recent titles, I would suspect AMD-only as well until nVidia can get their popsnizzle together.
Why the hell, after all these years, can't they just make a simple port of the toolset to Mac? It would probably take someone half an hour. If the game runs, the toolset will. This is just silly. Just hit the Mac switch in the compiler and do it.
The toolset was originally written using a Borland IDE, which only targets Windows. Releasing on Mac/Linux would involve rebuilding the entire toolset in a new cross-platform IDE, which is outside of the scope of the Enhanced Edition.