The purpose of 11.3 is to ensure feature parity between the high-level (D3D11) and low-level (D3D12) APIs on the same OS. What happens with 8 and 7 in particular remains to be seen, but adding features to a platform not getting D3D12 would at best be a secondary goal of 11.3.Wait what? This was confirmed where? I understood the whole point of DX11.3 etc would be to bring DX12 features to older OSes, including 8 (especially considering 7 doesn't even support full 11.1, i doubt it would get 11.3 either)?
Meanwhile, major feature additions often require a new version of WDDM. And as MS has already found out, backporting WDDM is problematic.