Well, of course that can be done. And I even believe in the easily - because the complete hardware abstraction is in the Darwin kernel. The system is nicely layered - everything higher up is written in Objective-C (okay, older parts from the old OS world like Appleworks certainly in C++ or C). The porting effort for OS X to Intel should really be very minimal. And I even think that within Apple there could well be a machine with Intel chips running ported OS X. The question is whether Apple would benefit from it: Apple doesn't just make money from supplying software (or an operating system among many), but also and especially from sold hardware. If Apple now switches not only the used components but also the CPU to standard parts, what kind of control or defense would Apple still have against the clones so despised by His Highness?
Because one thing is clear: an open clone market would be anything but beneficial for Apple. They need their own hardware market - and the availability of cheap alternative devices would disturb that very significantly.
At MacGuardians you can find the original article.