>This big difference between the Kernel Modules and GNOME Extensions is that we in the kernel community do not encourage out-of-tree modules. Indeed, they are strongly discouraged.

It's not different, it's mostly the same with extensions. They're strongly discouraged unless you're able to track upstream and follow the release. If someone can't do that, then don't depend on them to make an extension. You wouldn't make such a person a kernel maintainer of a key feature either.

>That might be a fine answer, if the extensions API were treated like the system call interface, where we do keep things stable.

That comes back to what I was saying earlier. The system call interface is very small and very limited compared to the total size of the kernel's API. It's not the same as the GS extension API, which is a huge API that allows access to various internals. The equivalent to create a "syscall API" in GNOME shell would be one of the options I said earlier -- "Limit the extension API to a small group of stable functions" which would not please you either, because that would essentially be removing APIs and would cause even more extensions to break and become impossible to implement.

Of course if you decided to stabilize everything then you would be stuck with a project where you can't refactor anything -- imagine a future for Linux where you have eBPF hooks across every function and internal structure, and you can't change any of them ever, because those kernel structures are now external API accessed by userspace. If you want GNOME to stabilize their internal API, that's really what you're asking them to do. Is that a good explanation of the problem? I'm trying to explain here why this is actually a really nasty technical minefield, and ultimately has little to do with release policy, or with any particular architectural decisions made by GNOME. There are basically zero active open source desktops that have a comprehensive and stable plugin API. KDE doesn't do it here either -- these particular areas are not even possible to change there with plugins, you're just lucky enough that the core workflow works for you.

>unless they like being randomly broken at a distro upgrade.

This is not strictly true. Just FYI, I've seen some GNOME-based distros that are starting to bring certain extensions into their release cycle, and make those part of the upgrade. But of course that falls on the distro to support the extension and do the testing before they ship, so the extension has to pass a certain quality and usefulness threshold first for that distro's users. If you get stuck using a GNOME-based distro in the future, you may want to check what their policy is there, you may be surprised (although I don't think any are shipping 2d workspaces).

>Xfce and KDE support 2-d workspaces as core features.

That's great, you should use those if those are what you like. But here is my perspective: If some XFCE or KDE developers (who know how to implement 2d workspaces) wanted to spare some time to revive the 2d workspaces extension in GNOME, and keep it working during distro upgrades, and support you doing what you like, I don't think any GNOME people would have a problem with that. Similarly, if it were possible in a reliable way, I don't think anyone in KDE or XFCE would have a problem if some GNOME developer maintained an optional XFCE or KDE extension to make those use a GNOME-style workspace overview, for those who prefer that design.