Thanks to a blog entry by ZDNet's Mary Jo Foley, there has been some fairly wild speculation flying around the Internets that the next version of Windows, due in 2010, will be modular. That is, you will be able to pick and choose components to have at install time, allowing you to build a version of Windows most suitable to the task at hand.
It would, I suppose, look something a little like Linux, where you have the core kernel and a range of optional add-in services and applications built around that. Theoretically Microsoft could set up a licensing system wherein you only pay for the modules you use.
While the concept is appealing, especially for 'light' systems like the Asus Eee PC, it's hard to really imagine Microsoft implementing this in a way that's meaningful for the consumer. Is it really going to allow us to not have IE installed, or remove legacy support systems (which comprise a huge chunk of Windows bloat), or not have Windows Media Player? That seems unlikely to me, even in light of all of Microsoft's antitrust issues (but it would be great if it happened).
What's more likely is that OEMs will have the option to build a version of Windows without some of the services that most people never use. They might even have the option to remove some of the support applications in the OS (like mail or photo viewers), though I doubt many would do so given the way these applications add to the perception of value. And most will probably be unwilling to remove anything that might increase their support call load (removing some backwards compatibility, for example, could eliminate a lot of bloat, but cause all sorts of compatibility issues).
What we might see (and I'm speculating here) is elements like IIS, Windows Defender and Windows Firewall being folded into modules, and those modules will be attached to individual subscription services.
In any case, we'll probably know a good deal more about this in the coming months, as more of Windows 7's internal workings come to light. [ZDNet]