my guess around april 2013, it may look simple from customers point of view but right now they are top notch and they cant really put more into these cards, 7xxx series only came out because of new manufacturing process i.e. 32nm whihc enabled higher performance chips to be made on small pcbs etc.etc.
so expect new series when a completely new technology comes out, who knows maybe quad chips cards, like the 9800gx2 have two boards of twin chips connected together, that'd be awesome but the 4 8 pins might not be enough and we would need new cooling technology, it all comes down to the development in Micro processing technologies, but if a 7970 isnt enough for you go ahead with a quadro, cant have better gpus then those cards