Writing graphics code in a unified model is quite a bit different from the conventional x86 model.

It isn’t. The difference is pretty small, and it’s just optimizations for when copies can be skipped and not a radical change in the approach of how rendering is done.

Intel would need their own equivalent to Metal if they wanted to do a similar move.

Not at all. If big-ish changes were required, they could be exposed as Vulkan extensions.

I don’t know enough about Vulkan to say if it’s compatible with this kind of approach

Of course Vulkan, the graphics API used on all modern phones except Apple’s, supports using integrated graphics efficiently.

It is closed in the sense that all the ISO specs are closed - you have to pay a decent sum of money to see the specs, and you’re not allowed to just copy them and show them to people that haven’t bought access.

They are not closed like HDMI though - if you implement them, copy constants from the specs into the Linux kernel for example, that’s fine. Having actually open standards like Wayland would be a lot better though ofc…

No. Source 2 still uses some X11 specific stuff and has to be ported over to Wayland before it can work Wayland-native