Ubuntu unveils its next-generation shell and display server

I think perhaps you're confusing client side decorations for client side allocated buffers? Client side decorations come up again and again, but we've never really talked much about client side buffer allocation.

Client side buffer allocation refers to how the client allocates its own pixel buffers directly from the kernel memory manager instead of going through the server. It's an implementation detail in the mesa side of Wayland and it's not something we ever really made a big point about. It's all covered by the wl_drm interface, which is private to mesa, defined in mesa and not part of core wayland. Other driver stacks would define their own wl_$chipset interface and allocate and exchange buffers whereever and however they want/need to.

And it's not a matter of "Wayland adding support" for server side buffers. It's not a feature in itself, it typically means that your hw or driver has restrictions on which process can allocate memory. The misconception here was that because the mesa integration code allocates buffer client side, other drivers wouldn't be able to allocate through the server.