On Windows, Vulkan support is provided by the IHV graphics drivers from Nvidia, AMD etc. On Mac, Apple themselves ship the drivers (incorporating some portions of IHV code, but ultimately all under Apple's control).
If you're using a newer Nvidia card, you can download and install much more up to date Mac drivers direct from Nvidia's site. Yes, Apple bundles their own drivers but there's nothing stopping hardware vendors from shipping their own Mac drivers.
That still wont change the version of OpenGL supported by the driver as far as I know. If someone has OpenGL 4.5 working on OSX I would be very interested in finding out.
