will not solve issues with compositors not having it

Many compositors already have patches for explicit sync which should get merged fairly quickly.

graphical libraries not having it

Both Vulkan and OpenGL have support for explicit sync

apps not supporting it

Apps don't need to support it, they just need to use Vulkan and OpenGL, and they will handle it.

Wayland doesn't implement sync of any kind, they probably meant to say "the Wayland stack"

Wayland has a protocol specifically for explicit sync, it's as much a part of Wayland as pretty much anything else that's part of Wayland.

Nvidia is not the only driver that needs to implement explicit sync.

Mesa has already merged explicit sync support.