Proton has the energy of open source clones of video games.
There’s a reason games aren’t made for Vulkan, even on platforms like Android.
It’s not just because there is a lack of market share.
Valve’s immense resources would be better spent on making Source Engine work for more game genres; itself support Vulkan better, or even default to Vulkan on Windows; make it fully free. If they really felt strongly about this.