Moving the config option out of the Linux staging area is signaling that the Radeon kernel mode-setting support is now officially ready for prime-time and its driver is in a readied stated that is at least as good as the user-space mode-setting paths. The Radeon kernel mode-setting support initially entered the Linux 2.6.31 kernel with the TTM memory manager, but now two major releases later is declared ready. One of the few features left (besides R800/Evergreen support and other smaller action items) is proper ATI KMS power management support, which is being worked on.
This latest DRM pull request for the Linux 2.6.33 kernel can be read on the dri-devel list. The Intel kernel mode-setting support has been in the main Kconfig area of the kernel for several releases. With the Linux 2.6.33 kernel, the Nouveau KMS code for NVIDIA hardware has entered the staging area.