“Because Proton are not accepting contributions, they own all the copyright, so can make the code closed source again if they want to (that wouldn’t affect the already released versions, but future versions)”
They can’t do that actually. They can close the source, yes, but if they do they can’t then release the new closed-source version to the public.
Does the GPL require that source code of modified versions be posted to the public?
The GPL does not require you to release your modified version, or any part of it. You are free to make modifications and use them privately, without ever releasing them. This applies to organizations (including companies), too; an organization can make a modified version and use it internally without ever releasing it outside the organization.
But if you release the modified version to the public in some way, the GPL requires you to make the modified source code available to the program’s users, under the GPL. [Emboldened by me.]
Can the developer of a program who distributed it under the GPL later license it to another party for exclusive use?
No, because the public already has the right to use the program under the GPL, and this right cannot be withdrawn.
“They could likely take down any derivative on iOS, since Apple will always take instruction from the copyright holder, for GPL’d code”
Does the license prohibit this? Definitely. Could they get away with it? Probably. Though I’m uncertain Proton would go that far. I mean, if they wanted to prevent forks, they wouldn’t have released the source, let alone with the GPL3 license, which requires the right to make modifications (as that’s one of the Four Freedoms).
“Since the builds are not reproducible, there’s no guarantee that the binaries they distribute are built from the source code”
Technically true, I suppose, though again why they would do that is beyond me. If they didn’t want forks, they likely wouldn’t have allowed forks.
Again, this is all assuming I’m understanding the GPL FAQ page correctly. If I’m wrong, I would welcome someone smarter than me to correct me. :)
They can’t do that actually. They can close the source, yes, but if they do they can’t then release the new closed-source version to the public.
From the GPL FAQ page:
Alternatively:
Does the license prohibit this? Definitely. Could they get away with it? Probably. Though I’m uncertain Proton would go that far. I mean, if they wanted to prevent forks, they wouldn’t have released the source, let alone with the GPL3 license, which requires the right to make modifications (as that’s one of the Four Freedoms).
Technically true, I suppose, though again why they would do that is beyond me. If they didn’t want forks, they likely wouldn’t have allowed forks.
Again, this is all assuming I’m understanding the GPL FAQ page correctly. If I’m wrong, I would welcome someone smarter than me to correct me. :)