Just for clarification, the current driver *does* support shaders and most of the games running on them are using shaders. What they don't support is GLSL - only the ARB_vp/fp shader language. The changes to support GLSL and OpenGL 2.0 will mostly be made in the mesa drivers, not radeon/radeonhd.
Availability of kernel modesetting (actually the GEM/TTM memory manager that comes with kernel modesetting) was a pre-requisite for some of the GL 2.0 functions, and also a pre-requisite for the Gallium3D drivers which will be the most likely path to GL 2.0. Now that KMS/GEM/TTM are available in the kernel tree, work on Gallium3D is starting to ramp up.
It's probably a bit early to make schedule estimates... maybe check back in a month.