Back before the iPad 2 was announced, there was some speculation that it might have a “Retina” style screen at a doubled (horizontal and vertical) resolution of 2048×1536, based on some extra-large assets found deep in the OS. That turned out not to be the case, but I still strongly believe it’s in the future for Apple’s tablet, and now a mega-sized Twitter image from iOS 5 lends further credence to the rumor.
The image (sent by @frankrockz to TechUnwrapped), backgrounds from within the Twitter .framework, are indeed 2048×1536, and exist alongside the existing 1024×768 assets. But they are the only ones found so far, suggesting that iOS 5 isn’t going to be the one that ships with this mythical display. It’s also entirely possible that it’s a desktop asset, but Apple’s 16:9 displays aren’t right for it. The fact that it’s a semi-transparent PNG means it’s an overlay, probably for a centered notification.
It could also be a mistake or fabrication, but with a precedent set in the iBooks asset, it seems more like an oversight. We’ll check around ourselves and see what we come up with.