If you subtract GNOME from the set then things become a lot more sane. "Compositor-specific extensions" are really "everyone besides GNOME extensions." The system tray extension isn't KDE-specific. Sure, window positions might not be available at all (because they don't make sense for a TWM), or a user might not have a system tray bar (or you might be on GNOME). However, if they did have a system tray it would be the StatusNotifierItem protocol. Ideally, these should be handled like other platform features like accelerometers etc.. That may not be possible, either way a lot of them can safely noop.
> [Article] For Avalonia, this means "Wayland support" isn't one implementation, it's potentially dozens. We're not just writing a Wayland backend; we're writing a GNOME-Wayland backend, a KDE-Wayland backend, a Sway-Wayland backend,
If you're making per-WM backends then you've fundamentally misunderstood how extensions are supposed to work. Other Wayland client libraries do not have a independent backends for KDE, Sway, and GNOME. Maybe quirks would be needed because you're attempting to support an existing UI library - but those should be few and far between.
IIRC Avalonia supports Vulkan as a rendering backend? Wayland protocols are the same line of thinking as Vulkan extensions.
wlroot and smithay are good examples of what extensions are used in the real world.
The whole idea of granular and independent extensions is pretty stupid across GL, Vulkan and Wayland. It makes more sense to have a handful "tiers" or "profiles" which guarantee a specific set of features (eg how all other 3D APIs do it) - e.g. Wayland should have a "desktop profile" instead of dozens of optional extensions needed for desktop scenarios, other profiles could be "mobile" and "kiosk".
What? No, that's not the case. Yes, different Wayland compositors often support different extensions, but everyone has the basics (Wayland core, xdg_shell, and probably a few others). You need one backend, and then you can support extensions to implement more advanced features, but you of course have to be able to continue to work without any extensions present.
Yes, there are some features that might require a different extension on GNOME than it does on KDE (for example), but you don't need a full "backend" to handle those differences.
As someone who has always been skeptical of Wayland, frustrated with its shortcomings, and who has written both a compositor and XEMBED-workalike library for Wayland, it just feels like author is trying to play up the difficulties for PR purposes here.
More likely you have to use a GNOME Extension (as in the plugin, not a wayland extension), or maybe a gnome-specific, possibly undocumented D-bus protocol.
