The iPhone 4 and iPhone 4S’s Retina Displays are already ludicrously pixel packed at 326 ppi, but even so, that’s only enough pixels to make it so that the human eye can’t resolve them when the phone is held twelve inches away from your face.
Apple can do better, and maybe someday they will, thanks to Japan Display’s new technology which squeeze 651 pixels per inch into an LCD screen. Their latest display has a resolution of 1280 x 800, the same as the existing 13-inch MacBook Pro, but is only 2.3 inches across.
That’s just one ppi from a true pixel doubling, which Apple has done for iOS devices to maintain backwards compatibility amongst apps and UI elements. If Apple picked this technology up, they’d finally have a display that was “retina” in the truest sense of the term… albeit, at four times the impact on the GPU..