Since the introduction of the GPL3, there's been a steady purge of GNU software from OS X.
Is it all GNU software that's being purged, or just the GPLv3 licensed stuff? If the latter, I can't say I blame them. The former case can go either way but I guess it's good to future-proof early.
The copyright holder can do anything they want with the license of the software, including change it. What has been released under older versions of the license cannot be taken back, as millions of people received the software under the old license...so if you received a version of Emacs under GPL v2, you have every right to continue to distribute it under the terms of that license, and you have no ability to alter those terms (since you are not the copyright holder). But, the GNU foundation (who holds the copyright for Emacs and all GNU software) has every right to alter what license they distribute new versions of the software under.
A lot of people have a lot of weird superstitions about the GPL. It's probably useful to read the license sometime. It may also be useful to acquire a basic understanding of copyright law, if you are a software developer.
Long answer: One of the conditions for contributing code to the GNU project is assigning copyright to the FSF. That means they're legally the sole copyright holders for all software they distribute. The official reason for this is so they can pursue GPL violations in court without involving the actual authors of the code. It also permits them to change the license on any of their software. Finally, there are various reasons they might be able to do this anyway even if they didn't have the copyright assignment rule, so long as the new restrictions didn't conflict with whatever license the original software was distributed under.
They can change how they license it from this moment on - but any copies they've already licensed continue to be licensed the way they were.
So if they licensed it to you as GPL, and then say "From now on, shareware is the way forward!" then you can continue to share yours as GPL, fork it, etc.
Well it's more likely than you might think over a span of a couple decades...
But, I think if they were to go rogue it would be a matter of forking a GPL-licensed version of the software and continuing development on that under an open license.
I don't think it is likely at all even in decades, and if they did they would be sued by loads of contributors for violating their binding promise to adhere with free software spirit in future licenses. You get some guarantees when you assign your copyright to the FSF.
And all this is ignoring that most GNU programs are licensed under a GPL variant and any future version, so they would not need the copyright to upgrade the license anyway.
I'm not saying it's a thing that's going to happen, just that you shouldn't have some blind faith that it won't ("I trust they won't do such a thing"). I'm pretty sure RMS would agree with the sentiment.
Basically all FSF-curated projects ask for contributors to assign copyright to the FSF. Which means the FSF ends up owning the rights to all the code, and can (as the copyright holder) switch to a different license for new versions.
I very much blame them for their effort to ensure they can prevent users from modifying Free Software utilities on their own machines. What else would be the purpose of avoiding GPLv3? And breaking compatibility with user scripts and removing features in the process... Glad my macbook pro can still boot linux.
Is it all GNU software that's being purged, or just the GPLv3 licensed stuff? If the latter, I can't say I blame them. The former case can go either way but I guess it's good to future-proof early.