Allow me to entertain you with this idea, I've played on shards where you could talk while hidden the text was only visible to other hidden players(I think) Also, What if you could see hidden and Stealthing guild members.
You can whisper, as far as I'm aware, which can only be heard by people on the next tile. And i think it doesn't break hide. You need to type a semicolon ; then hit space to initiate a whisper.
Seeing hidden/stealthing guild members would be cool. You used to be able to speak while hidden back when UO came out, if I remember correctly.
I remember in my first UO days this was the case. Back in my what-the-hell-is-this-game phase where I was murdered a lot. I don't think it would have an impact in game but nor do I think I would use it. The hidden and stealthing guild members I don't really like...it seems like it makes the stealth assassin teams a bit too easy. I like the idea of forcing them to coordinate.
It seems like you're after the social aspects of communication while hidden/stealthing. /party does these things.
Honestly, I think its just one of those small things that add so much. Picture this, walking along in Brit and you see the words appear out of a street corner! ''Psst!'' you're thinking huh?! where did that come from.. then a thief comes out from hiding and a discussion starts.