I'll cast in my vote here.
I have a 2010 MBP 15" and I would sell it and purchase a MBA 15" as soon as it comes out.
My top reasons:
1.) I need the 15" screen space with hi-res (1650x1080).
2.) I have only used my Superdrive twice in the 2 years I've had it. I would love to drop the optical drive and have a lighter notebook.
3.) SSD. I couldn't normally afford upgrading my HDD to an SSD. Having the SSD built into the MBA really gives good value.
4.) Lastly, I can use it to slice bread.
I'd assume you haven't used the 13" MBA?
There are some problems...
1) The screen has lower color gamut, and thus not as vibrant/contrast as the Pro line. I'd assume the same thing to happen to the 15" MBA if it ever comes out.
2) The lighter and thinner body of the MBA 13" comes at the expense of a solid construct. I can easily bend and flex the thing... anywhere... even when it's closed. It only doesn't flex if I use a case, but then that negates the thin and light idea completely. A 15" MBA would be even worse, as it spreads even wider than the 13" Air. The flexing problem makes the Air feel flimsier and less stable than it actually is, which was why I switched back to a 15" Pro when I had the chance. Didn't want an accidental bending of a MBA on my conscience. Is it that easy to flex a MacBook Air? Yes, it is.
3) You can try something like the Seagate Momentus XT for the best of both worlds.
4) It's not razor-sharp thin, despite belief. Cutting stuffs with an Air is ridiculously hard, and yes, I tried. Not to mention the thing flexes, but I think I actually did mention that.
I'm curious as to why there are concerns over a 15" MBA product's durability?
1. It's made of Aluminum - most laptops would crack if dropped from a 6' man's waist height.
2. It would weigh considerably less: about 1.5lbs without the SuperDrive.
3. The front bezel, or front of the laptop facing the user when closed doesn't have to be tapered like the current 11/13" MBA; I doubt opening a slightly heavier lid would be as easy as those for a 15" MBA, but who knows.
Also since when did Apple make their laptops with "Sturdy" in the design or product theme?! Their never to be tough books and to be honest with all the "setup" threads on these boards, considering this site is the LARGEST worldwide Apple product fan forums, I highly doubt any user here would/has EVER risked their PowerBook, MacBook (Air/Pro/etc) to Any construction site, let alone a small kids playground with 15+ under 10 kids running around like they rule the world ... waiting for an accident to happen.
As I mentioned above, it's quite easy to flex the MBA 13". Perhaps it's due to the density of material, or Apple's attempt at lowering weight, or... whichever it is, the machine is extremely easy to flex. I had one for an extended period of time, and without a case, the screen would be pressed into the keyboard, leaving marks afterward. It could get to a point where the keyboard and trackpad would scratch the screen. But the bottom line is... it's just not as "solid" as a MacBook Pro.
And I think you meant to say 1.5kg without the optical drive? The current MacBook Air 13" weighs almost at 3lbs (1.25kg). There's no way a 15" Air would weigh half that.
Apple indeed never marketed their products as "sturdy", but that doesn't mean they didn't build their products well. It wasn't until the MacBook Air that there was a serious concern with build quality and long-term durability, all because the body is way too thin to hold itself up. The 13" MBA really shows the limits of what Apple can do with aluminum. I suspect they'll have to use carbon fiber if they were to make a 15" Air.