There is a class of extensions that were only created to allow efficient ways for translation layers to map to Vulkan.
This includes replicating legacy behavior that is challenging for drivers to implement efficiently. This functionality is not considered forward looking, and is not expected to be promoted to a KHR extension or to core Vulkan.
Unless this is needed for translation, it is highly recommended that developers use alternative techniques of using the GPU to achieve the same functionality.
Everything needed for transform feedback can be done via a compute shader in Vulkan. There is also a great blog by Jason Ekstrand on why transform feedback is terrible and should be avoided.