I haven't seen this one requested here yet, but maybe I missed it? One thing I'd like to see is the ability to put a small note up for the shared libraries with my friends so I could say, hey guys I just got Jurassic Park digital version, and now it's up for your viewing pleasure! or Merry Christmas! I'm sure this would be a very easy add on, and I'm surprised it doesn't already exist.
That's part of the use for "Recently Added" but, sadly, some clients don't get visibility of this section on shared libraries.
There are several existing requests for notifying users of new content or down times, etc. (In fact I have one as well.)
Right now, to get this functionality on Windows (Same device as PMS is running on.) you can use PlexNotify. For any device running Perl (including windows) you can use plexWatch/Web.
Neither options are "official" and can be... interesting, yeah, that's the word, if you don't know the ins and outs of how to do the particulars... Both options can send an email, sms or other type of messaging to your users.
Another option for Linux is PlexReport. This is pre-configured to send an email once a week to all of your users. (Sends the email out one week from the last time it was run.) I think it requires Python. You can find out more about it in the Linux Forum. You might be able to get this going on other devices, if you can get a Python install on the device.
In either of these options, the results can require some pretty heavy computer skills. All of them need to run on the PMS device in order to function, so can't be run on a 2nd computer. None of them change the actual Plex Web App or client interface to include this functionality. (Which is why we need to get an official version from Plex directly!)
None of those options are as simplistic or as user friendly as I am requesting.
I am requesting a simple news/updates box to type some text for it to appear on my plex server across all platforms.
The code is already there for them to do it, this would not take them a very long time to implement. Maybe they are not doing this for a certain reason that I haven't though of however.
The "Recently Added" as even simpler than you requested and is already in place. It shows you the most recent additions for each of your libraries that you have set up for it, all under the "On Deck" for each Managed User you have set up. It doesn't work for non-Home users, as they only get a "Shared Libraries" in the clients, but for managed Home Users it does work.
There is at least one request here for allowing other users to have the full "On Deck" and "Recently Added." So if you feel this is something you might like to see, put a Like on the first post in that thread to vote for it.
Where is the code for this ready to go? Do you mean the announcements? I think that uses a slightly different mechanism than what you are thinking of. It might be a bit harder to put in than you envision. I could be wrong, and usually am, at least 2 times a day. :)