Preview at WWDC likely in June, followed by September launch.
Apple Tweaking More Icons, Upgrading to HiDPI Sizes in OS X 10.7.4
AppleInsider pointed to TextEdit as one example, with Apple having upgraded its icon's previous maximum size of 512x512 under OS X 10.7.3 to 1024x1024 in OS X 10.7.4. But the larger image 1024x1024 is also listed as measuring at 512x512 points, indicating that it is indeed being targeted for screens measuring at double the resolution of current displays in each dimension.
Under OS X 10.7.3, the TextEdit icon file included four different image sizes: 16x16, 32x32, 128x128, and 512x512. With the move to OS X 10.7.4, the icon now comes in ten different sizes: 16x16, 32x32 HiDPI, 32x32, 64x64 HiDPI, 128x128, 256x256 HiDPI, 256x256, 512x512 HiDPI, 512x512, and 1024x1024 HiDPI.
TextEdit is not the only application to see an upgrade, however, as Automator has not only seen new HiDPI icons appear in OS X 10.7.4, but the icon itself has also undergone some tweaking. In OS X 10.7.4, the Automator robot has taken on a somewhat darker tone, with the glossiness being toned down and the previously silver arms, legs, and pipe now appearing black. The tweaked design had previously surfaced in developer previews of OS X Mountain Lion, but is now included in OS X Lion.
Automator icon in OS X 10.7.3 (left) and OS X 10.7.4 (right)
Like TextEdit, Automator has seen an increase in the number of image sizes included in the icon file, although to a smaller extent. Under OS X 10.7.3, the Automator icon included the same four basic sizes: 16x16, 32x32, 128x128, and 512x512. But under OS X 10.7.4, the new icon now comes in six different sizes: 16x16, 32x32, 128x128, 256x256, 512x512, and 1024x1024 HiDPI.
Retina-sized graphics have been appearing with increasing frequency in both OS X Lion and developer previews of OS X Mountain Lion. In line with those changes, Apple has been rumored to be launching a Retina display 15-inch MacBook Pro in the near future, with a 2880x1800 display measuring in at twice the resolution of the current 1440x900 display in each dimension.
As with the move to Retina displays on Apple's iOS devices, content would appear at the same physical size on these new displays as on current displays, but with much sharper image quality for applications bundling resources supporting the HiDPI mode. Even applications that do not immediately update their resources to HiDPI quality should see improvements in sharpness, as Apple will undoubtedly include the same font scaling improvements used in iOS to automatically scale up text in applications to HiDPI resolution.