While a lot of games developers are beating the DX12 drum, Valve's Dan Ginsberg believes there is not really much reason to ever create a DirectX 12 back-end for your game. Ginsberg is working heavily on Vulkan and claims the next-gen OpenGL is far superior than DX12 in various areas.
He said: "Unless you are aggressive enough to be shipping a DX12 game this year, I would argue that there is really not much reason to ever create a DX12 back end for your game".
He added: "And the reason for that is that Vulkan will cover you on Windows 10 on the same class of hardware and so much more from all these other platforms and IHVs that we've heard from. Metal is single platform, single vendor, and Vulkan... we are gonna have support for not only Windows 10 but Windows 7, Windows 8 and Linux".
His comments about DX12 start around the 1:40:01 mark in the video below.