I think it has a lot more to do with not enough aircraft having the product.

Let's say you buy YYZ-YVR-NRT in PY, and then once you arrive in YVR, you find out their's a substitution, and you're downgraded to Y. Now what? You've received part of what you paid for, but I'm guessing you wanted it more for the TPAC.

Or you buy it YYZ-YVR, and the one flight a day that had a PY cabin went mechanical, and now there's no way they can get you to your destination the same day in the cabin you paid for, even with hourly flights.

It would not surprise me to see a difference in price between preferred seats and PY in North America in the not too distance future. Whether that comes with any other amenities (food/drink) is another matter, but I don't see the current model surviving the year.