Yeah, but at what cost?
2 280s in load take 340-380W depending on how you measure already. As the 9800GTX+ obviously showed, the 55nm process for nVidia offers little in terms of improvement (I would say it shaves 10% off power max).
Even then, you'd have a card that's 310-350W at current GTX280 clocks, that can't manage a decisive win against the X2, especially at the usage levels of uberhighend (8XAA, no?)
nVidia has to swallow this one up for their own good.
Well NVIDIA doesn't necessarily need to score a decisive win. They just need to be more competitive than they are right now. If they don't do that by overall performance they need to do it providing more bang for the buck.