I'm too cynical to believe Microsoft, or any other shareholder-driven company, would adopt that strategy.
In fact, I don't believe that has ever been done. Take a look at Microsoft Exchange Server 2000 which featured NNTP and IM. By the time Exchange 2003 came out Microsoft deprecated NNTP and removed IM, yet kept the price the same. Only customers on Software Assurance got licenses for OCS, everyone else had to shell out a lot more money for that feature.
well i think the need to buy a different disk and re-install the OS just to add features is areally bad idea.
and if they can sell addons to the base how will that be something shareholders or the board would not want? the idea that selling the basic OS for the basic price != not making the same amount of money.
one of the flaws i saw in some of the prior versions of windows was having to many versions and not finding out what features / addons were really the ones that folks wanted to buy.
if users can pick what they want then MS might even be able to make more money by offering more stuff that folks want and will pay for.