I don't really understand the licensing issues that well, but if what the poster above you said is true, I wouldn't really want to have to sign software that ships with my computer when it should just run out of the box.
I believe that they are suggesting that Apple would be required to let you sign your own software if you do choose and give owners the right to opt to have their os trust software they OR Apple signed.
There is something that was addressed in the gpl community called tivoization.
Tivos dvrs were Linux boxes wherein they shared their source technically complying with the letter of the gpl but in fact locking them down so users couldn't modify the devices violating to many peoples mind the spirit and clearly expressed intent of the license.
This is if I understand correctly dealt with in gpl 3 which is what I think the poster is talking about.
Apple ios devices are non free in the same fashion as Tivos which is incompatible with gpl3
On macOS, you can run anything out of the box (depending on security/gatekeeper settings) and you can replace or modify system executables (such as /bin/bash) if you turn off SIP (which is slightly tricky to do but can be done from recovery mode.)
Running your own customized /usr/local/bin/bash is easy of course, and package managers like MacPorts or Brew make it simple to install various shells including the latest bash.
On iOS, however, there might be an issue, as you have to sign executables with XCode, but unfortunately Apple reduced free developer provisioning profiles from one year down to two weeks in order to block third-party app stores and malware, and to get more people to sign up for the paid developer program. Moreover, there is also no Apple-sanctioned way to modify system executables that I am aware of.
I wouldn't even classify turning off SIP as "slightly tricky". You boot into recovery mode, open the terminal, type in two words, and press enter.
Besides, this is separate from the GPLv3 question. You can absolutely recompile bash and replace macOS's version with your own, so I don't understand why this is a problem for Apple.
If Bash were also being used on iOS that would be different, but I'm quite confident that will never happen.
But preventing ALL Macs from turning off Gatekeeper and SIP? I think that would be unpopular.
I know it sounds crazy, but they have for years now been taking steps - like this - which nobody seems to find a rational cause for, but which step by step seem to remove obstacles of technically, legal, or user expectations in line with making OS X an app store only platform, and if possible completely replace OS X with iOS.
1) Gatekeeper makes it harder to run malware; unsigned executables don't run by default, and signed malware can have its developer keys revoked by Apple.
2) SIP makes it harder for malware to modify system files.
The obvious "rational" business benefit to Apple is that:
3) Gatekeeper makes it harder to sell Mac apps without Apple getting a 30% cut
It's certainly possible that Apple has intentions other than to make the platform better and a discussion can be had on if the tradeoffs are worth it, but it's ridiculous to claim that there are zero benefits to anyone but Apple.
We're talking about what Apple could be planning that would violate the GPLv3. As long as the signing can be disabled by the user, there shouldn't be a GPLv3 violation.
I also expect zillions of helpful nieces/nephews would flip that checkbox for their uncles/aunts, and, accidentally or on purpose, leave it that way.
Even if that isn’t true, making it harder for malware to flip that flag already is a rational reason to implement it this way.
I do worry very much about SIP becoming impossible to disable some day. Don't ban knives because people might cut themselves.