If Apple does not bring to the market the full screen touch ipod it will be a clear sign that Apple is not the company that it says it is. "Our products are the best products in the world"- Mr. Steve Jobs (basically every year he works at Apple).
It would be a clear case of Apple NOT making the best product it could.
If Apple falls into the easy option of 'limiting' some products it makes in order to protect other products this shows a real flaw in their thinking and a real limit in their ability to create products.
Why not make the ipod some super product giving it some excellent features that distinguish it from the iphone and that make it desirable?
Really, such backward thinking from Apple... if it is the case!
Would you still buy the more expensive Macbook Pro over the Macbook if the only difference was the screen size?
The iPhone is clearly a premium device, it has heaps of features because it helps it do what it does best, managing your day and for listening (and seeing) your music. Apple would need to create a whole new line of (niched) iPods.
If you carried both your iPod and your mobile phone with you everywhere, which one would you use more? Now combine the two and compare it with just using an iPod. So if the 6G iPod had a multi-function touchscreen how often would you be using it? Probably even less than the 5G iPod.
So, basically you're asking Apple to make a iPhone, without the wireless capability.
Given that, I think that people would buy into a fully functional say, iPod Pro (think PDA) with wireless b/g. But this wouldn't get Apple any ongoing revenue from phone companies.