I support most of this idea. I think there should be a small caption within the ShoutBox itself. No modding to the page, simply a caption to a tooltip style message at the top, spanning the full width of the SB, but only being tall enough to display a simple 1 line message, 2 if you wish to give in depth information.
Example line 1;
"Game Maint, Web Mall Maint"
Example line 2(optional);
As pointed out by the main suggestion the GSs are constantly flooded with "server down?" "I can't login" or "maint?" which must be irritating. This can mostly be solved with a message in or around the shout box, you can not expect every player to stop asking, but it can only help the situation that is still ongoing.