Is gallium now deprecated within Mesa? The way this post is written it seems that way but I could swear I had read a similar post recently about other hardware in mesa leveraging gallium to get to a working driver faster.
Gallium is still the way everything else is implemented (OpenGL, Direct3D 9, video decoding, OpenCL) for drivers. One of those drivers is Zink which implements the Gallium OpenGL state tracker on top of Vulkan and another is D3D12 which does the same on top of Direct3D 12 (for WSL2). Not every driver supports every state tracker, in general all you can count on is some version of OpenGL to be supported (4.6 for Zink, 3.3 for D3D12).
Edit: Gallium is not only not deprecated, but it's also used by basically every GL driver withing Mesa these days.