Well, we do have things like USB, Bluetooth, Intel HD Audio, ACPI, and so forth, all of which are standards. VESA is still good enough to get an unaccelerated framebuffer set up and going. Network adapters are usually at least supported by Linux, so there's some open-source reference implementation somewhere. (NDISwrapper is mostly a thing of the past, thank goodness...)

Accelerated graphics is probably the biggest remaining disaster, honestly. At least with Vulkan/DX12 we might be getting thinner drivers...