It is possible? Yes. Will it happen? No
There is no reason for dxvk to implement d3d12 when vkd3d-proton exists, which the devs also contribute to.
In regards to APIs lower than d3d8 see https://github.com/doitsujin/dxvk/issues/4199#issuecomment-2278648019
Older versions than D3D8 are part of DirectDraw. That's why there are no plans to support anything older than D3D8.
As for D3D12: the API is more low level than older D3D APIs which is why it does not make sense to implement it as part of DXVK. That said, @doitsujin is one of the primary developers of VKD3D-Proton. (https://github.com/HansKristian-Work/vkd3d-proton/graphs/contributors)
Or DXVK is integrated with VKD3D, just as D8VK is integrated with DXVK
vkd3d-proton and dxvk have different licenses and programming languages. Besides that the APIs are different enough, d3d12 is much lower level as @K0bin wrote, that it makes sense for them to be separate projects.
If it can be integrated, there is no need to install multiple different versions to reduce conflicts
There aren't any conflicts anyway and installing DLLs from two different projects is really not such a big deal...
If that's too much work for you, just stick to Steam games. Steam will handle the installation for you as part of Proton.
As for the support of D3D7 and below versions, it is to consider the minority needs of mobile phones, and dxvk is used in the mobile phone wine container. ...
Phones are not a target platform of DXVK.
I know that this DXVK is to meet the needs of playing computer games without a computer, not to mention cloud gaming ...
Is it possible to support d3d12 so that you don't have to install vkd3d or support older versions than d3d8?