I think I've fulfilled the OP's request for SSH.
I'd imagine there would want to be some discussion over sending messages to the Orbiters and the web admin.
The web admin is easy, because it could just display a banner of some sort. But when you start to think of acknowledging it, setting a database flag perhaps? It starts to get more complicated. Same with MessageSend, you don't want the script running every time someone logs into SSH or every time the cron runs and MessageSend-ing to all the orbiters. There needs to be some kind of acknowledgement flagging. Then there's formatting for colours, font weight, etc. It'd need to be different for each output, console/web/Orbiter.
The script I've written specifically caters for the SSH MOTD. While it could be expanded, I'm more of a KISS kind of guy, that script in that location shouldn't be messing around with other things. It's purpose is just to generate and output an MOTD fragment.
For further discussion, the script looks at a fictional URL http://svn.linuxmce.org/svn/trunk/lmce-dynamic-motd
there would need to be a policy governing it's content and update frequency. I pointed at SVN because it has a good audit trail, which I think is important if your going to be sending messages to so many systems. It also means we can use raw files and not have to set up a fancy administration system for the messages.
I forgot to add that my script does have a dependency on wget.