some people would get really upset if their code was released under a license that allowed it to be put in proprietary code.
the FSF has the ability to allow that (make GPLv4 equivalent to BSD, proprietary company takes code and moves it to it's own license)
and before you protest and say that they have promised to never do anything like that, remember that they made a special clause in the license to allow GPL documents that were in wikipedia before a specific date to be moved to a GPL incompatible license.
They have the ability, the only question is will they.
I am not saying that they will, only that they have the ability to do so.