GPS and BT are the only two "big" features that are even remotely likely. 3G isn't going to happen. 3G = cell phone. iPod != phone.
I can see GPS to get the touch working with location aware apps, that makes sense from both Apple's, developers, and users prospectives. I would think that they would make a better GPS antenna and better GPS chip to get "real" GPS positioning, since it won't be able to rely on cell towers for added precision.
I can see BT for some new Apple branded stereo wireless headphones and tethering to other cell's to get mobile data for apps.
Aside from those big features, I can see a volume rocker button and a speaker being added. Speaker would be useful for all the iPod games being release, along with the obvious YouTube and other video watching stuff, and better alarms with your iPod.
A vibrating motor would be something in the realm of possibility as they could use it to add some haptic feedback to the interface.
Camera would be completely useless since it sucks compared to any other pocket sized camera and you don't have 100% of the users connected to the internet 100% of the time so there's no instant sharing making it worth using.
But 3G is just a complete impossibilty. If you have a 3G chip/antenna in the device it's a phone, just without a mic. There's absoultely no reason to do it. You have to have a data plan from a cell provider, and all the same electronics so there's no distinction between that device and a phone other than a $.25 microphone. It just makes no sense. Please stop trying to convince yourself.
Now, once the 700mhz spectrum is up and running as a highspeed wireless data only network I can see an iPod with that, but we're looking at 3+ years down the road.