Such a move would enable MicroSoft to sell MS Word to all current Linux owners; in effect, Linux would become coopted by Windows if they added that code. Every Windows developer would be able to market their software to every Linux user, all without having to spend a dime on porting old code over to a different platform.
It's the Borg strategy; Linux would become assimilated. MicroSoft and MS developers would all gain a larger market to market new sales.
At that point, no one would *care* about Linux. It would no longer be unique. It would just be another way to run Windows applications...a "free" way, as opposed to the most recent way. Yet even with a "free" OS, users would still have to pay to buy those MS applications.
...And the more advanced users would hardly want old Linux platforms rather than cool new Longhorn platforms, so it wouldn't even kill off MicroSoft's existing OS sales.
Trust me, ten years from now what I'm saying will be labeled as "obvious" to everyone.