Yes, SPIRV->DXIL does seem tempting and worth exploring. Very recently I learned Mesa has such a tool, spirv2dxil, though unsure how robust/featureful it is compared to HLSL->DXC->DXIL.
>>slimsa+aU3
Nope, I said vkd3d has a DXIL->SPIRV converter (since it runs dx12 on vulkan), not a SPIR-V->DXIL (which would be running vulkan on dx12).