Apologize if this is already available but I don't think so... also sorry if it has been suggested, but it is tough to search for so I couldn't find anything.
Basically, I think it would be nice to have the ability to leave notes/announcements for all users or even specific users. Example - my family all uses my Plex Server to watch home videos in the library and connect to it all of the time. I would like to be able to notify them that the server will be down while I am out of town (or replacing computer, etc.) Yes, I realize I could simply email them but for somebody with a ton of users, I think this would be handy. Another example - if you add a really bad movie you could leave a note to the effect of 'I haven't seen this, but Joe wanted it added.'
Anyway - just thought I'd throw it out there. Thanks devs - keep up the great work.