Hi Acrolvm,
I've done some software development, but never developed any 3D application, so, I may completely be wrong in the following.
My understanding is the the API (Direct3D or Vulkan) manages everything that is display on screen at low level. So, basically, implementing Vulkan support in addition to Direct3D would require to rewrite most if not all graphical improvements provided by RWEnhancer, which is quite a heavy work, and even possibly the sound improvements, as these API tends to manage this part too.
So in short, I believe this would require some heavy development, and thus would take quite some time, at the cost of implementing new features, debug, etc...