Maybe in a couple of years' time. If another MS OS were released now, and couldn't go on a CD, they'd have to do it on two CDs, as DVD is nearly, but not quite, the standard for the majority of PCs.
Incidentally, quite a few operating systems come on a number of CDs. They contain plenty of extra software as well generally, but just thought I'd drop that tidbit of info into the conversation :-)
