They explained how difficult it is to transition to the DX12/Vulkan way of doing things if you're already heavily dependant on the DX11 way of doing things. They've done DX12, but it's not really been any improvement yet because they're not structured to take advantage of it.Unity is seems really behind the times IMO. That engine is basically perfect for Vulkan, why not?
Then again, this is the engine that does not even support Fullscreen modes at runtime..
I wouldn't worry about a lack of Unity support in Vulkan for a little while at least. A lot of their work on DX12 support should help if/when they add Vulkan support.