I think that there will in fact be a G5 iMac before the end of this year. My personal opinion is that the new iMac should be a headless machine. There are tons of advantages to doing this.
I think that there should be a 1.4 to 1.6 GHz G5 iMac using the new architecture like the PowerMacs only scaled down a little. Maybe only use a 4x AGP, with regular PCI slots, no FW800, 4x SuperDrive, PC2700 DDR RAM (exp to 4 GB), 800 MHz FSB. It would be great to see a sub $1000 G5 Mac. This is one of the great things you can do with a headless iMac. I think it would sell like the original iMac did. It would certainly attract more Windoze users. They would have a fast G5 processor, with the new architecture, expandability, and you can get any monitor you want. Plus if you want to upgrade you don't have to pay for the display everytime.
I have a 1 GHz FP iMac and it has a beautiful display, but its not upgradable, and if I want to upgrade my iMac I basically have to buy a new iMac. This isn't right, and I think Apple needs to look at this.
I think there will be a PowerBook G5 by at least this time next year, maybe MacWorld SF. That will also use at least part of the new architecture with the high bandwidth.
The eMac/iBook should use this new G3 that IBM is developing and market it as the G4. Speeds ranging from 1.2 to 1.5 GHz with a 400 MHz FSB. The eMac should have basically the same specs only using DDR RAM and this new G3 processor.
I'll get off my soapbox now... Any opinions welcome!