Removing the "cross application snooping" is X11 is.. difficult. In a sense, that is equivalent to removing piping and redirection from shell -- "for security".

Now, many people don't mind, but I certainly mind. That is why I still use X11. Definition of trust... you trust what you must. "Operating systems have to be less trusting". But my Operating System must trust me. I give it no choice in the matter. My Operating System must not override my Trust decisions.