It looks like we can expect NVIDIA to unleash next-gen GPUs this year, with the GeForce GTX 800 series to be revealed this year. Sweoverclockers is reporting that NVIDIA will launch both the GeForce GTX 880 and GTX 870 sometime in Q4 2014 - so between October and December.
While the GeForce GTX 880 and GTX 870 will be based off of NVIDIA's second generation Maxwell architecture, it will be on the 28nm process - not the 20nm process that we expected. TSMC has started volume production of the 20nm node for everyone, but this should start being spun on new GPUs in 2015 - something that will provide a large jump in performance, thermals, noise and much more for both NVIDIA and AMD.
Another interesting part of this news, is that NVIDIA has reportedly canceled the production of GM100 chips, in favor of the GM200 chips. These new GPUs are still based on the 28nm process, so it will be 2015 before things really ramp up for next-gen GPUs. This means that the new GeForce GTX 800 series are cards 'for now,' and intermediary product before NVIDIA can ramp up 20nm-based products next year.
We might see a few parts based on the 20nm process released under the GeForce GTX 800 series, but time will tell. These parts might arrive as something new, or old - such as NVIDIA bringing back the Ultra branding - which would be based on the 20nm process. This is my personal thought on the future, something I hope to see NVIDIA do. Release the intermediary product - GTX 880 and GTX 870 - and then unleash the GTX 880 Ultra based on the 20nm process before they drop the truly next-gen, 20nm-based GTX 990 (or whatever it arrives as).