Except I think the author has this wrong: it won't be "Air" but "Pro", and will be thicker than the Air and more expensive.
On a purely numbers basis, the difference doesn't seem significant (hence how I talked myself into the purchase), but there's a massive "human scale" threshold that's crossed in that difference. IMO, an 11" MBA feels more "like an iPad" in those respects vs. a 13" MBP very much feeling "like a computer".
Not knowing more about the specs of this hypothetical 12" machine, I'm theorizing it'd be approximately halfway between the 11" and 13" Air in size/weight. That of course may not be right, but it seems unlikely to be way off. So, while my comparison is hypothetical and imperfect, I don't feel it's quite apples and oranges, either.