It's Apple Style

We may see the next iPad in a carbon fiber body and Front facing camera but there is a minimal or no chance of having retinal display for the next iPad.

According to Ryan Block calculations, 9.7 inch iPad Retina display would exceed the capabilities of current mobile device technology.

330 pixels per inch (PPI) works on the iPhone 4 precisely because it's such a small screen. Each pixel must be rendered, and the Retina display packs 614,400 pixels at 960 x 640. The same processors are used to display graphics on the iPhone 4 and the current model iPad (the iPad display is 1024 x 768 = 786,432 pixels).

Converting the iPad display to a Retina display would result in a huge number of pixels, leaving graphics processing hardware completely overrun and done.

Macbook Pro 17-inch: 1920 x 1200 = 2,304,000 pixels
Dell 24-inch monitor: 1920 x 1200 = 2,304,000 pixels
Apple 27-inch Cinema Display: 2560 x 1440 = 3,686,400 pixels

Retina display for iPad 2 is possible if Apple come with new powerful graphic processor.

Src: [The iPad Guide]