There wasn´t any "last time", since process technology didn´t allow for it to happen. To reduce costs and improve margins, while keeping performance at least on par, they really need(ed) a half-node with all options (Low-K) of it´s bigger brother. An optical shrink based on 90nm to 80nm will surely take some time, since libraries need to be adjusted and you have to take account of the time for another tapeout. Costs aren´t really relevant in that equation if they want to continue with R580, because when there is enough volume (cost-cutting measures could easily be taken) those starting investments really do seem like nothing at all.
R600 is some ways off, i´m afraid.