Though a bit of a ways off yet, it appears NVIDIA is already prepping up for Shader Model 5.0 with their latest SDK 10 providing some clues as to the not-too-distant future existance of hardware to use it, most likely G90 being the first.
More about it over at Nordic Hardware.
NVIDIA recently launched its SDK 10 (Software Development Kit) and inside of this you can find some clues to the graphics circuit manufacturer's view on the future. SDK 10 namely has CG profiles for Fragment50, Vertex50 and Geometry50, which means that game developers now have tools for making games for Shader Model 5.0. This should mean that game developers will be able to study SM5.0 and experiment with the compiler and code for new games, which in turn should mean that Shader Model 5.0-capable hardware is on the horizon. According to VR-Zone this new hardware could be G90, which according to rumors will appear before the end of the year.