@jwz I know this is an old post, but I thought of it when I saw this: https://old.reddit.com/r/ABoringDystopia/comments/1jkwcbx/if_i_leave_my_vizio_tv_idle_it_plays_calming/
Granted it's Vizio, not Google so not sure if it would fit into the XScreenSaver privacy policy, but I am pretty certain that XScreenSaver would not serve up propaganda in between relaxing images during the idle time of my display device.