The iPod Touch 4g was released on September 2010. Since then, we never saw any major update to any of the iPods. So it is possible that Apple will update the device this fall.
Rumors showed that the 5th generation iPod Touch will have an all new design using the in-cell touch display technology. The same one that will probably show up on the next iPhone.
Macotakara reports that Apple made the iPod's display bigger, from 3.5 to 4 inches. While the other specs should be the same as the iPhone 4s's.