But the point he was making was that there is no need for DX12 because Vulkan works everywhere else.
Right now Vulkan is only supported on custom Android 6 forks for Samsung S7 and NVidia Shield, Android 7, GNU/Linux and Windows on a restricted set of graphic cards.
Hardly a market to target for game developers that want to reach as much eyes as possible.
Just think how much more popular Windows 7 is compared to DX12. Xbox One is nothing in comparison.
Windows 10 users are already 45%, with around 41% having DX 12 GPUs + plus around 20 million Xbox One units.
As for market size of Vulkan, some S7 and NVidia shield as part of 10% Android 6, 0% on Android 7 until it reaches stable and of course those other 55% users that might have a Vulkan compatible card.
Because all three are APIs which try to provide a lot more control over the GPU to game developers. And I wouldn't know of any other similarities that DX12 and Metal share...