There’s some problems with the OpenGL renderer in some distros of Linux, so if you’re able to add an option for switching to Vulkan it would be appreciated, and some shaders are broken on Linux, like the post processing stuff.
Vulkan requires additional and lengthy programming, I'm not so sure if you have to create entirely new shaders for it, as Dani is using Unity, but I believe Vulkan and OpenGL use completely different programming languages which may make it harder to program.
I do agree with your suggestion, but it's often best to know what developers can and cannot do. I have no knowledge in Dani's programming skills, but I am certain that it may take a while for him to do this.
As a unity developer myself I can say that it’s pretty trivial to change between rendering backends in unity, unity does the bulk of the work.
Unity uses a modified version of HLSL for shaders, modified so that it can be compiled to all the other backends. (See: https://docs.unity3d.com/Manual/SL-ShadingLanguage.html )