So the 320 and 328 are (almost) identical and yet there is a sizeable price difference. 2 possible conclusions from there:
* The 328i is insanely profitable
* The 320i will be at a loss or no benefit for BMW, and is just intended to fill the market and prevent other brands from gaining followers
I suspect the second one. Also, the 3 bangers is expected to deliver the same 180hp, but think of the sale pitch on the US market.
You would have had a 300hp i6, 240hp i4, and introduce a new 180hp i3. People would have been trashtalking about brand dilution and ridiculous undermotorenwerke for ages, damaging the new engine sales and possibly the brand image.
Now look at the sales pitch when introducing the 180hp i3, when the 180hp i4 exists in the lineup already... Same hp, gets 30% mpg increase, that's like you can actually make a point that the i3 is superior technology, instead of being watered down crapola.