A lot of people would! MS would lose marketshare to Apple and OS X.
Can you imagine the OEM race to write proper drivers?
It would be a smashing bestseller, even if Ballmer tried to throw a chair at everyone who bought it . . .
You said -- "A lot of people would! MS would lose marketshare to Apple and OS X"
It doesn't make any sense for Apple, for the kind of company that they've made of themselves. They're a hardware company and that ("selling the Mac OS X") would not benefit their hardware. Thus, it will never happen.
You just have to know what kind of company Apple is and why they make their decisions that way.
Regards,
Star Traveler