How much risk do you think there is in putting a Unibody (aluminum) MacBook Air in there without incurring dents from the camera gear due to handling and bumps encountered in normal use?
Since there is really no padding in the sides of the bags, just the thickness of the material itself, the laptop would be minimally protected. Depending upon the way you work out of the bag, how much of the time you'll be carrying the laptop in the bag, how the bag is handled, and how much gear you you carry, you'd probably dent the laptop eventually. But if you're just carrying the bag with the laptop in it from home to office, and then removing the laptop and working out of the bag you'd be less likely to damage the laptop. Personally if I were traveling with the bag, and laptop, I'd get to my destination leave the laptop in the hotel room, and then go shoot. And since the MacBook Air is thinner, it might fair better.