Edit: Actually nvm, that's not what I was saying. You're misunderstanding something; weston implements the wayland protocol/interfaces, because clients need to talk to it via them. If there is functionality for eg. a screen recorder that's built into the compositor, as is the case with wcap, there is no interface because there is no client to talk to, since the code paths lie directly in the compositor. You'll find that there is no "screen capture" interface in wayland. An interface is needed when an outside client (such as is the case with IM support, see text input protocol extension) provides the service and needs a standard way to talk to a compositor for resources / locked down functions.
No announcement yet.
RealVNC Remote Desktop Wants To Support Wayland