One of the more intriguing differences uncovered so far is the inclusion of a Broadcom BCM4329 combination Wi-Fi/Bluetooth chip, which supports the 802.11n Wi-Fi standard in addition to 802.11a/b/g standards. The iPhone 3GS and the second-generation iPod touch utilize a different BCM4325 chip, which supports only the 802.11a/b/g standards. While Apple has apparently not activated 802.11n capability in the iPod touch and it is unknown whether it will choose to do so in the future, the new iPod touch hardware does appear to be capable of supporting the standard.
Speaking of rumored-but-not-delivered:
iFixit has also revealed that there is a small empty space at the top of the device (approximately 6 mm x 6 mm x 3 mm) where an iPod nano-style camera could fit. The iPod touch does not appear to be thick enough to adequately house an autofocus camera as found in the iPhone 3GS.
Would we have wanted an iPod touch with VGA video like the nano, but no 3mp stills like the iPhone 3GS?