That's not accurate. A wayland compositor can implement plugin support and delegate stuff to external processes; this is how weston works. You can swap out one shell for another, and if you want you can implement a shell that itself delegates out the dock, window decoration, etc. each to different processes. But the defaults will and should be that arbitrary apps cannot in any way snoop on or interfere with the user's interaction with other apps, so obviously any app that wants to do so will have to get authorization and use some interfaces that aren't part of the normal protocol for presenting an app to the user. You're not "being constrained by [the] architecture" of the standard implementation in any way that's not completely justified.
You're suggesting that compositor- and shell-specific plugin interfaces can replace X11's desktop protocols? I understand that X11's security issues had to be fixed: I just wish that the new system had preserved some of X11's support for heterogeneous environments and not relied on the extensibility of specific compositor implementations.
Wayland tries to be a simpler and smaller system than X11. For it to specify equivalents to ICCCM and EWMH would be way beyond its scope. But there's nothing preventing such equivalents from being standardized; it just won't be part of Wayland, since Wayland also wants to target use cases where such things would be inapplicable. If there ends up being a proliferation of wayland implementations that support pluggable components, I think we'll definitely see some quick standardization of the necessary interfaces. But at the moment people are still working on successfully using one desktop environment at a time, so good support for the mashups will have to wait.
