Ilia Mirkin, an independent open-source developer that's becoming one of the most prolific Nouveau developers in recent times, landed a bunch of Nouveau NV50/NVC0 Gallium3D driver code this morning. The NV50 driver supports the GeForce 8 through GeForce 300 series while the NVC0 driver supports the GeForce 400/500 Fermi hardware and beyond.
The newly exposed extensions by the Nouveau Gallium3D code include ARB_texture_gather and ARB_texture_query_lod. The Intel Mesa driver had already supported both of these OpenGL extensions while the R600/RadeonSI Gallium3D drivers supported the latter extension as well.
With those latest commits, here's what the OpenGL 4 extension coverage looks like for the main Mesa/Gallium3D drivers per the latest GL3.txt TODO in Git:
GLSL 4.0 not started
GL_ARB_texture_query_lod DONE (i965, nv50, nvc0)
GL_ARB_draw_buffers_blend DONE (i965, nv50, nvc0, r600, radeonsi, softpipe)
GL_ARB_draw_indirect DONE (i965)
GL_ARB_gpu_shader_fp64 not started
GL_ARB_sample_shading DONE (i965)
GL_ARB_shader_subroutine not started
GL_ARB_tessellation_shader not started
GL_ARB_texture_buffer_object_rgb32 DONE (i965, nvc0, r600, radeonsi, softpipe)
GL_ARB_texture_cube_map_array DONE (i965, nv50, nvc0, r600, softpipe)
GL_ARB_texture_gather DONE (i965, nv50, nvc0)
GL_ARB_transform_feedback2 DONE (i965, nv50, nvc0, r600, radeonsi)
GL_ARB_transform_feedback3 DONE (i965, nv50, nvc0, r600, radeonsi)
Most of the work left is with the GL Shading Language changes along with GL_ARB_tessellation_shader, GL_ARB_shader_subroutine, and GL_ARB_gpu_shader_fp64. I'm becoming more hopeful that we'll see OpenGL 4.0 open-source support out of the Intel Linux driver in 2014, but after that there's still a lot of work to be done for the OpenGL 4.1, 4.2, 4.3, and 4.4 specifications.