iPhone profit per model: $400-$600.
iPod profit per model: $100-$250 ($200 cost plus $250 profit or $250 and $250 for 50/50)
Example: If WI-FI adds $75 (assume charging $100 over similar device without (even if they dont make it) minus $25 component cost) profit AND many more sales (this is hard to predict) could, as one example, have 1 million more sales at $200 profit and 2 million sales with an additional $75 profit which would mean $350 in additional profit. If half of those 1 million sales came from CANNIBILIZING the iPhone, that would still only mean $250 in lost iPhone profit, and a NET gain of $100 million dollars, plus a new market niche.
What the above example shows, however, is that it could go either way, depending on cost, price, and total sales of the new iPod. Apple has experts probably working on those very models, and of course they know how much it costs them (and then will set the price). While iPhones make a ton of profit, iPods make a good amount too, sell more, and will not cannibalize iPhones at a 1 to 1 ratio. Apple can probably predict sales at different prices and components pretty well, and adjust what they build and sell to make selling profitable regardless (WI-FI would have a leg up, because they would be able to sell more).
Assuming the technology is no problem, then what may really shape this debate over WI-FI isnt the profits shown above, but the strategy (https://forums.macrumors.com/showthread.php?p=4114327#post4114327) that they may consider for the long-run and how an advanced iPod (aPod?) would fit in.
I think there are few major assumptions here that make the maths a bit simplistic to have one or the other "i" device. Cannibalization could be much less for these reasons:-
a) A Touch iPod with a HDD with more/all of your music would tempt people to buy both devices.
b) A Touch iPod that has WiFi (with or without HDD) and becomes a Smart universal remote for your


c) If they do something to the Touch iPod with HDD like make it also a video camera, give it a high MP camera, add BT Stereo headphones, share music in proxity to others with these iPods or Macs, or some other unexpected wildcard then having both becomes tempting
So I think its pretty compelling to give it WiFi.