krh and robster have both done work on this: https://github.com/krh/gtk/tree/csd https://github.com/krh/gtk/tree/shm https://github.com/rbradford/gtk/tree/wip/csd
this doesn't concern Wayland protocol itself. And for the implementation, I'd recommend to track the needed changes on Gnome's bugzilla instead. I'm closing the bug.
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