The pull request probably wouldn't be accepted because it's a major change and no other Mutter contributors are interested in reviewing such a patch or dealing

The pull request probably wouldn't be accepted because it's a major change and no other Mutter contributors are interested in reviewing such a patch or dealing with the (far-reaching) effects of it. GNOME is just the nonprofit open source project and it doesn't really allocate resources or have resources to spare -- it's got to be a volunteer who works on this who has enough resources to do it in a way that doesn't mess it up for everyone else, maybe that's Canonical who can do it, I don't know. There is also the option of implementing it first in one of the forks (Elementary, Budgie, etc), testing it out for a while, and then submitting it later after it's known that it works and doesn't break everything. Getting upstream to accept a 10,000 line patch is not easy under any circumstances. There are other window managers that don't support server side decorations, I don't know why people always single out GNOME. Weston is important too, it's not often used directly but it's used as a base for other implementations -- if your app is busted and has no decorations on the reference implementation it can hardly be called a working Wayland app. Server side decorations do have a use case but they're not equivalent to client side decorations. I used to think they were until I tried to implement them in a window manager, now I see server side decorations as mostly a broken concept unless it's in very specific circumstances. The toolkits and apps have to implement client side decorations if they want to ensure the correct behavior everywhere, it's unavoidable.