References to a new iPod touch have been found in the first beta of iOS 5 by iFans forum member shamrock.
well, I was rooting through the OS and I stumbled across this in the fairplayd daemon. This is on the iPod touch 4 on iOS 5 beta 1.
The screenshot below shows references to an iPod4,1 and an iPod4,2 device. The current iPod is 4,1; however, the 4,2 device doesn't exist, yet.
Judging by Apple's typical naming scheme, the next iPod release will be a minor update. A major update would get a model identifier of 5,1.