In the Vulkan space, this on-disk shader cache is less useful than on the OpenGL side. Vulkan has the concept of a pipeline cache that allows for objects to be re-used between pipelines and between runs of an application or game. But with Vulkan it's up to the application for allocating and managing these pipeline cache objects.
Timothy Arceri is adding an on-disk shader cache to the open-source Radeon Vulkan driver as a fallback for applications/games not managing a pipeline cache.
With two patches that amount to very little new code, this on-disk shader cache can be introduced to RADV by taking advantage of all Mesa's common infrastructure for a shader cache. He didn't provide any figures though whether this RADV shader cache should be that useful if existing Linux games are already making use of the Vulkan pipeline cache.