Probably just a rumor.. but I think it would be pretty silly to release a "595" with the 28nm cards so close.
A Slovenian gaming news site that looked into some of the PCs running Battlefield 3 at Gamescom mentioned the name "GTX 595". This couldn't have been in error, because the site goes on to mention that the GTX 595 is "a dual-GPU card that is not yet out," adding that "NVIDIA provide[ed] special drivers for EA gamescom to improve a little gaming experience (and probably reduce bugs )." Those could have been early drivers that can run the card. According to older reports, the idea behind GTX 595 (as it's now being referred to), is to strengthen the VRM circuitry of GTX 590, to perhaps facilitate higher clock speeds, and try to create a clear performance lead over Radeon HD 6990. Nothing else is known about the GTX 595 at this point. In our opinion, Battlefield 3 launch (late October) could serve as a good launchpad for a new high-end SKU.