Ben Skeggs, the Nouveau DRM maintainer at Red Hat, has already been successful in getting the moderately-demanding Xonotic first person shooter game running on a GM200 GPU. He also got GLAMOR working for providing 2D acceleration over OpenGL. The Piglit OpenGL regression tests for Mesa are also beginning to run on the modified Nouveau DRM driver and patches that have yet to be mainlined for Mesa's Nouveau NVC0 Gallium3D driver.
Skeggs made the comments today via the Nouveau IRC channel. The kernel-side work is likely to land for the Linux 4.6 kernel while the NVC0 Gallium3D changes will have to wait until the next Mesa release in three months time due to the Mesa 11.2 branching set to happen this week.
Update: It looks like the code will hit Mesa 11.2 after all - That Was Fast: GM20x Maxwell Support Already Hitting Mesa.