Chinese website GamerSky has posted up photos that they are calling a GeForce GTX 880 engineering sample, and boy do they paint quite the picture. The prototype that is in the photos below has some incredible specs behind it, with 8GB of RAM to start things off.
We should expect two variants to launch, with a GeForce GTX 880 with 4GB of RAM, and another with 8GB of RAM. From here, we have 3 PCIe power connectors, two 6-pin connectors and a single 8-pin connector for a total power draw of 375W. This is an insane number, but we are looking at a 28nm-based Maxwell GPU, and not the 20nm GPU that will pave the way for lower power draw and temperatures.
We should hopefully see the GeForce GTX 880 materialize before the end of the year, with a refreshed GTX 990 on the 20nm process expected for 2015 - this is me guessing here, but I think we'll see it happen.