This idea creates a serious chicken-egg-problem.
Two or three popular engine code bases sitting on top of Vulkan isn't enough 'critical mass' to get robust and high performance Vulkan drivers. When there's so little diversity in the code hammering on the Vulkan API it's unlikely that all the little bugs and performance problems lurking in the drivers will be triggered and fixed, especially when most Unity or Unreal game projects will simply select the D3D11 or D3D12 backend since their main target platform on PC is Windows.
Similar problem to when GLQuake was the only popular OpenGL game, as soon as your own code used the GL API in a slightly different way than Quake did all kinds of things broke since those GL drivers only properly implemented and tested the GL subset used by GLQuake, and with the specific function call patterns of GLQuake.
From what I've seen so far, the MESA Vulkan drivers on Linux seem to be in much better shape than the average Windows Vulkan driver. The only explanation I have for this is that there are hardly any Windows games running on top of Vulkan (instead they use D3D11 or D3D12), while running those same D3D11/D3D12 games on Linux via Proton always goes through the Vulkan driver. So on Linux there may be more 'evolutionary pressure' to get high quality Vulkan drivers indirectly via D3D11/D3D12 games that run via Proton.
Vulkan is mature. It has been used in production since 2013 (!) in the form of Mantle. I have no idea why all the Vulkan doomsayers here think it still needs a half-to-whole decade to be 'useful'.
I run all my windows games on Vulkan.
I don't think those lists are complete, but they seem to show the right relative amount of 3D API usage across PC games.
Proton is amazing and Wine project deserves your support.
Says who? Why?
It looks long term stable to me so I don't see the issue.
No current gen console supports it. Mac is stuck on OpenGL 4.1 (you can't even compile anything OpenGL on a Mac without hacks). Devices like Android run Vulkan more and more and are sunsetting OpenGLES. No, OpenGL is dead. Vulkan/Metal/NVN/DX12/WebGPU are the current.
Edit: By the same logic you could argue that C89 is dead for new projects but that's obviously not true. C89 is eternal and so is OpenGL now that we've got decent hardware independent implementations.
There are literally dozens of in-house engines that run on Vulkan. Not everything is Unreal or Unity.
This is not true in the slightest. There are loads of custom 3D engines across many many companies/hobbyists. Vulkan has been out for a decade now, there are likely Vulkan backends in many (if not most) of them.