The GF104 is a powerful chip that runs cooler and is much more efficient than the GF100. The GF104 is only used in the GTX 460 while the GF100 is used in the GTX 465, 470, and 480. Now it seems NVIDIA is gearing up to put the GF104 in the GTX 470 to make it run better, perform higher, and stay much cooler. Keep this under rumor for now as NVIDIA has not confirmed anything, but it does make sense to pack a GF104 chip into the GTX 470 since the 470 has relatively low clocks compared to the GTX 460. The GTX 460 has one full cluster disabled though even with the cluster enabled, a GF104-based GTX 470 would only have 384 SP and be on a 256-bit interface. The GTX 470 has 448 SP and is on a 320-bit interface, so a GF104 version would need to make up the deficit by having a higher clock speed. If this card does come to fruition, odds are that it will be called a GTX 475 and should easily outperform the current GTX 470.
There are also rumors that NVIDIA will replace the GTX 480 with a dual GPU card consiting of two GTX 460s on a single PCB. If that comes to pass, then NVIDIA is taking ATI's approach to video cards since the high end from ATI essentially has two HD 5850s on one PCB.
The GTX 460 has basically replaced the GTX 465 so I can see why NVIDIA wants to replace the existing GF100 products with new GF104 ones. Only question is if NVIDIA had the GF104 ready to go so quickly after the launch of GF100, why launch three cards with it when it could be replaced by a more efficient product mere months later?