Campaign Battle messages happen pretty often as well, but there is a chat filter for them. I think that works pretty okay.
They could also show them only in the Escha areas I guess, like Bastion (remember that!?), but it would still be nice to be able to filter them out.
Perhaps an item would be okay too, but I wonder how much unnecessary server stress it would cause what with all the people querying for it (I suppose the majority might still go by the unity messages though).
I'd like the Campaign Battle sort of option most, probably, or maybe an NPC that would talk about it (I think the Abyssea people in towns can tell about Bastion... or I remember crazy).
It would be a nice change, though I personally can live with checking the areas, or flipping the chat switch for a time (tend to be in Sylvie's chat since no other alter ego quite does what she does, but I also tend to keep the chat off if it's being full to give a spot to someone else, unless I really want to see it (would be nice to know about Mireu in some way still though)).