The Iris devs are making a new mod called Aperture, that will fully replace Iris/Optifine and then some. Hopefully the newer shaders will be able to take advantage of a lot of modern hardware features like ray tracing. It is going to be a real pain to translate existing shaders though (speaking as someone who will have to do that at some point)

The saving grace is we get some semblance of shaders in game that are officially supported and they look quite nice so far. No needing to install a mod loader, shader mod and download different shaders to get stuff working. Vulkan does afford more low level performance and extra functionality over OpenGL though, it will be quite interesting to see what mod authors come up with when we get start getting other vulkan based shader packs. It’ll be a slow process but exciting times!

My only worry is the potential duplicate effort on mod authors having to work with both Vulkan and OpenGL simultaneously. Vulkan is a bit of a mess of a spec and also extremely low level so it requires a developer with a very solid understanding of the graphics process to work with.