The folks over at WCCF Tech have shown a leaked slide from Nvidia, and according to this, Nvidia won't be launching any more GTX 700 series discrete desktop graphics cards throughout 2013 after the release of the GTX 760.
The slide shows the lineup of products for May, June, and Fall 2013. The lineup for June is exactly identical to that of Fall 2013. The top graphics cards for these two are the GTX Titan, the GTX 780, the GTX 770, and the GTX 760, ordered from most to less powerful. The slide clearly shows the GTX 760 replacing the GTX 660 Ti. The GTX 670 doesn't appear in the slide, even though its performance lies between that of the GTX 660 Ti and the GTX 770.
While this may be disappointing to some enthusiasts out there, it does show that Nvidia is confident in its current lineup of graphics cards. The good news is that for anyone who still has recently bought a GTX 660 or lower, they need not fear that their card will be outdated soon. It will be good for at least another six months, and there is no indication yet as to what will happen early 2014.