I also really think that bluetooth would be a great addition to the iPod. That way, you could use the iPod as an external media storage and save space on your computer. It also makes wireless headphones and sharing between iPods possible.
I don't see why you would need bluetooth to backup files to your iPod. You can do it already with USB 2.0 which is more reliable (no paring), more secure (wired is always more secure than wireless), and way faster.
You have to be careful what you add to a product. Once you add in a feature it becomes very hard to take away. Remember when Apple dropped Firewire? There was a $#itstorm beyond belief of which I'm still a little miffed about to this day myself.
You also have to consider how to gain back the battery life lost by adding yet another chip to the circuit board.
I don't see a major use for wifi. Its not like it has Safari built into it or something. Again, you have to make up for lost battery life from adding another chip to the circuit board. You also have to try and keep costs down as well. The more you add do it, the more expensive it gets. Also, there's that thing I mentioned before about it being hard to take away features once you add it on.