wayland's main purpose is to isolate ~~malware~~ proprietary software running in a container, which Xorg doesn't allow (unless of course you run nested servers).
It wouldn't be too bad of a goal if it had feature parity, which it still doesn't have.
X11 does have various ways to restrict access (one of which ssh does use for instance) and some more advanced security extensions. But as far as I can tell there has never been that much motivation to widely deploy any of it.
