We can only conjecture what the update might be. But many of us expect an update in November.
So let's go ahead! Both sizes will be replaced with a 13" widescreen case, with 1GHz 750GX IBM G3 processor, GeForce 5200 graphics, Airport Extreme. Base RAM 256MB across the line. The case will be spiffed up with a little bit of chrome here and there. The keyboard will be stiffer and not openable. And most-awaited of all, the ethernet connector will be more rugged, with a little extender cable to reduce direct insertions.
Good model will have CD-RW, better model will have Combo drive and Bluetooth