A bluetooth iPod would be sweet!
Despite the criticism of bluetooth in terms of sound quality and syncing, I think there are 3 very useful applications for bluetooth in the iPod.
First, most of us aren't audiophiles and there are certain situations where even the best set of headphones would be overkill. One of those places is the gym. Even with headphones on, there's interference from all the noise in the gym, so even if sound quality isn't great, average sound quality would be good enough and well worth not having wires getting in the way all the time.
Second, bluetooth would be useful for remote applications whether it be to control FrontRow or as an Airport Express remote. I use Salling Clicker with my Treo and it's great for controlling apps on my Mini that's hooked up to my LCD TV.
Third, if Apple does come out with a touchscreen video iPod and at a minimum opens up the platform for developers, Bluetooth would be a great way to get internet connectivity to the iPod. If I recall correctly, EVDO has transmissions speeds of about 500-700Kbps and Bluetooth is somewhere around 730Kbps. My Sprint EVDO service is awesome! I'd love to be able to establish an internet connection through my phone to do light web browsing, run Dashboard widgets, send SMS text messages, etc.
I've always felt if Sony had opened up the PSP for more third party development and provided information to allow the construction of keyboards and other peripherals, the PSP I think would dominate over the DS. I think Apple would be extremely smart to encourage people to write apps for the iPod and I would hope they'd think about providing an SDK that works with XCode. I'd also like to see them clean up the PIM apps that are already on the iPod and add mobile versions of Safari, Mail, and Dashboard. I think the hardware on the iPod is more than powerful enough to run applications such as these.