From a business stance, I can easily see Apple shying away from making the iPod Touch 4th Gen like the iPhone 4. A part of me thinks that the iPhone 4 gave Apple product differentiation from the Touch that Apple was "looking for" with this new iPhone 4, resulting in a "success" for Apple...
I see the same iPod Touch Design as the 3rd Gen, but better specs & maybe a camera/videocamera. Remember, all Apple needs to do - is make you replace your old one for something that is better, and/or have a wanted feature... A camera will do that for most. And, this year, more than last, a camera is feasible because of the new iPhone having a total new Design.
I predict, no new outer design, bump in specs, and maybe or maybe not a camera/videocamera.
I lean towards a non-HD camera/videocamera, because there is more product differentation due to the iPhone 4 having a total new Design & HD Vid. I'm betting they will have this camera, to increase sales yet again...