I really don't think there is going to be an update anytime soon. I really don't expect an iPod update for another 4 to 5 months. I really don't see what they could update on hardware. If there is any update, it's most likely going to be a software update which will be available for all iPod users.
The current drives aren't fast enough to support FireWire 800, a color screen is just a ridiculous idea, and 20Gb is the biggest drive available at this time. The only hardware update I see feasible is a line-in jack for recording. But, I don't think that'll happen until Apple makes an OS X iApp for simple audio recording.
I too was waiting to get an iPod, but I decided to get one for Christmas. It's the best decision I ever made. Get it now! You'll love it. And, if something new comes out, sell it on eBay and buy a new one.