I think if the FSF could get away with a clause akin to "once licensed under the GPL, this software can not be licensed under any other license for distribution, and it's license can not be changed by the copyright holder".
But that wouldn't fly. Ever. At the end of the day, the copyright holder still gets to change their license whenever they want, and the license itself can't deny that, because it would never hold up in court.
It wouldn't fly, because to the copyright holder, the license simply doesn't apply. At all. You only need a license if you're restricted by copyright law from doing what you're doing, but copyright law doesn't restrict the holder themselves.
But that wouldn't fly. Ever. At the end of the day, the copyright holder still gets to change their license whenever they want, and the license itself can't deny that, because it would never hold up in court.