Some (most?) programs expect a high level OpenGL GPU API, instead of dealing with Vulkan/bare-metal directly. Converting some very high level OpenGL calls to actual API is part of what is expected from the driver. To implement this, you would most likely require a high performance, high IPC CPU embedded in the GPU - a waste since you already have one in the system.

> The now open sourced nvidia kernel modules should do something similar I guess

Those open sourced nvidia kernel modules does this - it is "near-zero" as you describe - they just moved almost everything important to the proprietary binary blob loaded to the GPU.

> Rumors: AMD may be interested in RISC-V ISAs

Everyone is interested in RISC-V, not necessarily in user-visible RISC-V ISAs.