9to5Mac's Mark Gurman writes: "The 12-inch MacBook Air will be considerably smaller than the current 13-inch version, yet also slightly narrower than the 11-inch model. The new 12-inch version is approximately a quarter-of-an-inch narrower than the 11-inch version, yet it is also a quarter-of-an-inch taller in order to accommodate the slightly larger display. In order to fit the larger screen into a footprint about the size of the current 11-inch model, the bezels on the display have been reduced on all sides."
Why this matters: We already have an 11-inch MacBook Air... and a 13-inch, too. So, doesn't a 12-inch just seem unnecessary To keep up the MacBook Air's reputation of being ultra-light and ultra-portable, it makes sense to keep the Air's screen size at 13-inches or less. However, something smaller than 11-inches will just be too small. So, the 12-inch could actually fill that "just right" sweet spot nicely.
It's not all about the size
However, if 9to5Mac's design estimates are correct, this is the start of a new design shift for the MacBook Air. We'll see features that are slimmer and more compact than before, with an edge-to-edge keyboard, a modified trackpad, and a thinner profile (yes, the Air will actually be getting smaller).
Apple could also introduce USB Type-C on the new Air, which means it would no longer need a MagSafe port, as reports on USB Type-C indicate that it can be used to power computers. 9to5Mac believes this single port could be used as a sort of hub, allowing users to plug in multiple devices to the Air.
Of course, this is just speculation at this point--Apple has yet to announce a new MacBook Air officially--but 9to5Mac's artist renditions are pretty cool. Check out their full report for more details.