The announcement is pretty confusing since Mesa is used on Linux but Metal only exists on macOS/iOS. I guess this is only for Linux VMs running on macOS such as the Android emulator. Maybe it could also be used to run desktop Linux in a VM.
It's even theoretically possible to use the Asahi Linux hardware Mesa drivers on macOS, though actually doing so would involve hacking around undocumented APIs. I actually thought this was demonstrated before (during early testing) but I can't find it.
Someone else managed to get the RADV AMD driver working on Windows[1]. It is not fully merged upstream yet, but I think they would like to get it merged upstream eventually.
Windows 10 on ARM (maybe Windows 11?) also use Mesa with Microsoft and Collabora's d3d12 backend to run OpenGL and OpenCL applications on top of d3d12, for hardware that does not have proper OpenGL and OpenCL drivers[2].
And of course, it ought to be possible to use llvmpipe/lavapipe with off-screen rendering pretty much anywhere you can get Mesa to build, although in practice I believe SwiftShader usually nets you a lot better performance if it's applicable.
So Mesa is actually not used only on Linux, it can be used pretty much anywhere, actually ships with Windows, and of course many other free software operating systems also ship Mesa.
[1]: https://www.phoronix.com/news/RADV-Windows-XDC-2024
[2]: https://devblogs.microsoft.com/directx/announcing-the-opencl...
It weirdly sounds crazier than it is. Mike is an absolute legend for all of his work on Zink.
Edit: Clicked on your link and they are directly talking about work there. Serves me right for not reading it first.