Sounds like a great idea, but it'll have to be two things for most stations to bite on it: free (or very cheap), and using as little or less system resources as commercial IM software.
The current use of (unnamed messenging software has been great. Often, we'll get a few minutes lead time on a warning, valuable insight on what the NWS is thinking, and WSOs get from us immediate storm reports. (All media in a CWA join a chat room set up by the WSO, and it works very well 95% of the time.)
And, most importantly, we can run it simultaneously on a computer that's doing something else.
Bouncing ideas back and forth during an event has proven to be an advantage for all concerned than a one-way street from NWS to the media/public.