I think it's hard to see an iphone nano coming out, not to mention that rumors have been relatively quiet about a product that would be much more popular than the fatboy nano. It would chip away at their high iphone profits (and expensive 2-year AT&T contracts) while angering AT&T (unless it was exclusive, then it would anger everyone else). Plus, it would skip over the middle step of wireless internet (although it must have bluetooth), wouldn't have a phone, would lack the ease of the touchwheel (unless we're looking at rotary phone dials again). The iphone nano, while potentially much greater than the ROKR or current MP3 phones, seems like jumping into an already saturated (although far from perfected) market far too fast.
It appears far more likely that Apple will approach it like they did the IPOD and work on lowering the price and expanding the capabilities. When the AT&T eclusive contract runs out in, hopefully, 2009, then we could see many cheap iphones, but for now, don't bet on it, especially when an iphone nano will do little to convince anyone who didn't switch to AT&T for the iphone to do it now, which leaves them a much smaller market.
Wireless on the Ipod Touch (isn't it amazing that in the space of a few days it has evolved into talking about it like its already availible in stores), however, is a different story. While perhaps not likely, it is at least possible. While it would cut into the profits of the iphone and AT&T, and all of the other reasons people have listed above, there is one thing that I thought of today that makes it seem more likely:
There is nothing (technologically or even economically), that would stop them. They have done it, and they can do it. A wireless module would not cost too much extra if the touch already has OS X (as it would for multi-touch), and it would add internet and email/contacts synching for a low cost.
One year ago, I don't think we would be having this debate because Apple had always (in their computers as well) put the best technology in their products. The iphone has shown a new, more microsoftesque, version of Apple that could withhold something that would be easy (they had it in January), cheap, and would benifit a large number of people. Adding OS X just to have cover flow and multi-touch seems like lost potential.
Finally, Apple has come, for the first time since the launch of the original ipod, serious pressure from competitors (no, I'm not talking about the Zune). Sandisk, Creative, and others have created cheaper, more advanced devices, and Apple is already behind (for $79, the price of a shuffle, you can get a 2gb nano-esque creative Zen V that also plays video (although on a TINY screen)). The touch will catch them up in some regards, but the only way to stay on top (the cool factor, itunes compatibility, and style are becoming less of must-have options) is to jump ahead with a price reduction across the board and newer products that no one has.
So, Apple, we all know that you can do it, and you have not/rarely disappointed us in the past, so please make a WI-FI ipod and one with a large hard drive.
P.S. Maybe in the last few months Apple had time to focus on software, because the one thing that would really drive them to add wireless to the Ipod is if they came up with mobile itunes. Microsoft horribly dropped the ball, but I wouldn't bet on Apple doing the same . They could be updating the software for the Iphone (with this included) to address the many shortfalls that people have addressed and could use that as an opportunity.