Considering the extraordinary success of the MacBook Air in its previous and current refreshes, it doesn't take a particularly accurate crystal ball to predict where the overall laptop lineup is headed. Apple's buying power in NAND flash memory helps it deliver SSDs in portable machines at lower component costs than the competition, and the pure sexy factor of leaner, lighter (yet still powerful) notebooks is winning converts to the platform.
MacRumors believes a 15" ultra-thin Mac laptop is in the late testing stages at Apple, although the post doesn't nail down whether this beastie would be considered part of the Air or Pro lines. Likely as not, the larger laptop would skip the optical drive in favor of slimmer lines and longer battery life.
This 15" Air-esque rumor corresponds pretty well with what we're hearing, but with a few additional tidbits: chances are these will be the next MacBook Pros, not oversized Airs. There's also a 17" model in the works. And we might see them under Christmas trees, with a few weeks to spare.
If Apple can control costs on the SSD front and deliver Pro performance in a lean package (hopefully with a relatively full suite of ports, or a Thunderbolt breakout dongle), the Air-like Pro would be quite compelling.