That would be like running an Xbox emulator on an Xbox. You could just play the game without having to jump through a bunch of silly hoops and lose a bunch of performance due to the emulation layers.
I'm guessing you've never actually tried DXVK on Windows. It actually does help at times---while there is overhead in cpu translating DX9/10/11/12 calls to Vulkan, when a game graphics engine is bottlenecked by the lower thread optimized older DX versions, it can actually increase performance.
AMD generally benefits more than Nvidia with DXVK on Windows because Nvidia's DX11 drivers are far better thread optimized than AMD's. Also, Mantle was originally designed by AMD, so it wouldn't shock me if some of their old AMD-centric code is still in Vulkan.
I use it (DXVK on Windows) all the time on GW2 (built on DX9, has a native DX11 mode now) on my 6900XT/5950X. It makes a noticeable difference, even with the native DX11 mode now available. And its as simple as unzipping the tarball, placing the 64-bit dx11.dll + dxgi.dll files in the GW2.exe directory.
Heck, back when GW2 was still only DX9, there was a 3rd party translation dll created called "D912PXY" which translated DX9 calls to DX12 and it made a BIG difference.