The bolded line is the one I have been thinking for some time. If you look at the 13" MBA and the 14 & 16" MBP, they are basically in the body of a 12" for the Air and either a 13" or 15" for the Pro, primarily because of the minimal bezels around the displays. With the 13" Air, that gives you the portability of a 12" with the display and additional ports of the 13"
It is trending that way, but the size and weight difference between the 12" and the 13" Air is still pretty dramatic in real life. 2lbs vs 2.7lbs isn't a lot on paper, and the size difference isn't a lot on paper, but that 12" was light and tiny and it puts it in a different class than the Air altogether.
Whether or not a market still exists for the 12" is another story, but unless you've used both of these side by side you might not appreciate the vast difference between them.