There are no signs as to whether the chipset will be all new, an Nforce 3 if you will, or whether it will simply be an updated Nforce 2. There can be no doubt that the Nforce 2 is the chipset du jour for Athlon XP systems. It already supports a 400MHz FSB so, in theory at least, Nvidia could have sat on its laurels.
With Via snapping at its heals, it could be that Nvidia decided to move the market more its own way. There must have been plans for the update made quite some time ago, a chipset doesn't just spring up overnight. It may be that rumours months ago that the KT400A would be a dual channel chipset got the Nvidia engineers worried enough that they decided to work on something even better.
The most likely move is towards an updated Southbridge chip. There are a good few things that Nvidia would do well to get into the chip that require discrete components at the moment. Whatever it is, the update is certain to help keep Nvidia at the front of the AMD chipset race. ยต