It seems that we might only see the GTX 700 and HD 8000 Series appear in Q4 2013
Sweclockers has suggested that the next generation of AMD and Nvidia GPUs will be delayed all the way until Q4 2013. According to their source, the GPUs won't show up until as late as October 2013. This means that the current GTX 600 series and HD 7000 series will be around for a little longer, possibly expanding their lifespan by up to two years before replacement.
Regardless, we will be seeing new graphics cards soon. There are rumors of Nvidia's GeForce Titan, which might be released near the end of this month.
Moreover, there are rumors that AMD will also soon launch an official Radeon HD 7990. While there have been 7990s around for a while, none of them are official yet, just fabrications from different manufacturers.