It wouldn't be bad to use a different channel name for `VKD3D_SHADER_DEBUG`, though. Both `VKD3D_DEBUG` and `VKD3D_SHADER_DEBUG` can be very verbose, so it's not bad to selectively pick the one that you really care about.
Sure, but the debugging scheme in vkd3d would have to be changed first, the global variable approach doesn't allow supporting multiple channels when linking statically.