Surely easier than collaborating with Apple who are extreme lock-in proponents.

See for example projects like dxvk, which affected Vulkan spec:

* https://www.youtube.com/watch?v=1fU4w2ZGxH4&t=12m21s

* http://jason-blog.jlekstrand.net/2018/10/transform-feedback-...

Good luck for such thing happening with anything Apple related.

Spec development? No.

But for bug reports, debugging and fixing bugs in the shader compiler, validation layers, etc they are pretty responsive to issue reports and pull requests.