New 21.5-inch Retina 4K models expected.
"iPod3,1" References in iPhone OS 3.0 Point to iPod Touch Refresh
The "iPod3,1" reference was actually first discovered in the iPhone OS 3.0 beta back in March, along with entries for several other unreleased and/or unspecified products. Among those entries was one for "iPhone3,1", which appears to represent yet another iPhone model that has not yet been publicly released. Similarly, the mysterious "iFPGA", and "iProd0,1" products referenced at that time remain unknown.
These findings do seem to predict future models, as reports as far back as late January pointed to the existence of an "iPhone2,1" model, which eventually turned out to be the just-released iPhone 3GS. The next-generation iPod touch would certainly contain the updated ARM Cortex processor and improved Power VR graphics chip found in the iPhone 3GS. Other rumors have even claimed that the next iPod touch would also include a camera, which would presumably also be able to take video. This "iPod3,1" is most likely to be released around September based on Apple's history of iPod updates.