I think the laptops are going to be tapered when they add the metal plate at the bottom. Just like the Macbook Air, the vertical edge around the whole computer is uniform but the metal plate that makes the bottom of the computer is what gives it its tapered shape. The similar is going to happen to the Macbook Pros and Macbooks by adding a plate either metal or plastic, although they are going to be less tapered. The Pro might get a metal baseplate, while the regular Macbook might get a polycarbonate bottom shell for better wireless reception.
Apple won't make their computers like a rectangle again. Just look at the iMac, iPhone, iPod touch, and Air and you can see they are moving towards a new design direction for this generation's computers.