David Kirk, Chief Architect for NVIDIA says that there's plenty of mileage left in the G70 architecture, but that one day, when it makes sense to do so, NVIDIA will move to using a unified architecture in hardware. The design of NVIDIA G80 is based on unified shader architecture, which we should hopefully see appear as soon as next year.
G70 already supports Longhorn WGF 1.0 API so most likely G80 will support WGF 2.0 with improved virtualization techniques and new pipeline stages. The likely process technology choice for G80 is 90nm and the architecture is made for high core speed (~1GHz). G80 design is completed and waiting for ATI R580 when the time comes.
ATI has beaten NVIDIA to it, using the unified approach for their R500 Xenon within the XBox 360, which has 48 unified pipelines.