I can guess we'll these new models in 2007:
1) 3G nano with up to 20 GB of flash memory, but using the same form factor as the current model.
I don't see the next gen shuffle getting such a huge jump in capacity. I'd say 16GB at MOST, though maybe just 12.
2) 6G "conventional" iPod with 40 and 80 GB hard drives about the same size as the current 5.5G iPods. They will use the new touchscreen interface with a larger LCD display so you can watch videos clearly.
3) A true "video" iPod with 80 and 120 GB hard drives in a device about the size of unit designed to Microsoft Oragami specs (e.g., Samsung Q1 series) with a large screen and that new touch-screen interface. Unlike other new-generation iPods this new iPod will sport an IEEE-1394 interface for faster video transfer to device from desktop/laptop computer.
"Conventional" and "true video" versions both with 80GB? Who would buy the conventional one? Yeah, there might be a price difference for the bigger screen, but I think everyone would just opt for that. If they keep the conventional smaller sceen version around (for people who want more music plus the occassional TV show), expect to see a bigger space capacity difference between it and the true video version (targeted towards movie watchers, with a larger capacity model only).