David Kirk, NVIDIA's Chief Architect, said in an interview that NVIDIA may do a unified architecture in hardware in the future when it makes sense and when its possible to make the hardware work faster unified.
VR-Zone today reported that NVIDIA's G80 will already feature a unified shader architecture. This GPU is slated for next year.
The G80 design is ready and will be produced on a 90nm process. According to VR-Zone the chip will be clocked at about 1000MHz.