No QXGA (2048×1536)
Adding to the confusion has been speculation about the possibility of Apple still being able to offer a "Retina" display on the iPad while increasing the resolution by less than a factor of two, with observers arguing that the fact that an iPad is typically viewed at a farther distance than an iPhone would allow for an iPad "Retina" display at a lower pixels-per-inch than found on the iPhone. But others have argued that anything less than a doubling of the pixels in each dimension would cause significant problems for existing applications by not allowing them to be simply and sharply scaled up using pixel doubling methods.
Apple will not release an i-pad with exactly 2048×1536 pixels (QXGA), ever!
They didnt want to use XGA (1024×768) in the first place, but 960×720 instead (4:3 HD; the i-phone 4 has 960×640, DVGA, 3:2). Alas, manufacturers couldnt provide (multitouch) displays with this resolution at reasonable prices. Apple will hopefully correct this compromise with the second generation, introducing 1920×1440 (103 µm/px at 9.7 in diagonal), but perhaps only 1440×1080 (137 µm/px) or 1280×1024 (154 µm/px), aligning it better with their palm-sized devices.
Whatever they will do, the i-pad screen will become at least as high resolution as previous i-phones and i-pods: they had 156 µm pixels, the i-pad 1 has 192 µm (and the i-phone/i-pod 4 have 78 µm). That means the next version of the ipad screen (be it in 2nd or 3rd generation models) will be at least 1280×1024 if the physical size (ca. 200×150 mm) is retained.
They may, however, use XGA resolution with a smaller display device. A 7 inch (ca. 142×107 mm) XGA display, for instance, would have 183 px/in, i.e. a pixel size of less than 140 µm.
If Apple was not a US company, of course, the i-pad would probably not have a 4:3 screen, but something uncommon that is taller than √2:1, e.g. 17:12 or 13:9, i.e. ISO paper ratio plus vertical GUI chrome. On the other hand, the i-pad isnt really optimized for (scaled) letter paper (in portrait orientation) either, which has a ratio of 22:19 = 1,29.
The i-pad itself, by the way, is currently closer to a 5:4 ratio. If the screen needs to stay 4:3, Id like a 280×210 mm or a 300×225 mm screen in the future, although that is larger than current tablets.