I think once the kinks get worked out this is going to be one of the best things to happen to the game.
Regarding the sci-fi or other aspects, my suggestion would be that you have a whole host of scribes, and you are just saying "bring me all messages in X category".
I do want to echo the concerns about losing access to messages. Gaining access to older messages is fine, from my book, as if you don't want someone gaining that access, you don't use the official channel. There are plenty of ways around that, I'm not going to worry about it. But by the same token, if you lose access to the official channels, then I would expect to see a rise in pseudo-official channels where everyone in the realm knows that this player-created channel is the real Council discussion channel, just so they can keep the messages.