I'm going to jump back in on my own topic to comment on a few things that have been mentioned by others.
Designated party spokesperson: I like the idea that, for non-main-quest conversations, the party could have a designated spokesperson. In traditional D&D this would usually be the rogue/bard/sorceror/paladin (high charisma & conversational skills). It would help with things like getting lower prices with merchants and generally offering you favourable options in many conversations.
Skills in conversations. Despite what NWN2 does to you tactically speaking (i.e. bends you over and applies the lube) it did handle skills in conversation very well, especially in the MotB expansion. High enough Arcana, you can comment on the magic, high perception, you see/hear something etc. It's also something IWD2 did well with regards to intelligence changing your speech from "Defy me again and I will see you and your compatriots hang" to "Hulk smash".
Regarding stealthing up to a big-bad mage and backstabbing them, why shouldn't it be allowed? It's a legitimate tactic. If you REALLY don't want it to happen then have the mage already with stoneskin (or equivalent non-WOTC spell of uncannily similar name) to mitigate this somewhat or simply with his back to a wall... Wizards are meant to be smart right? Alternatively, if in a brightly lit room have the game apply location-based penalties to the stealth checks, have alarm traps on the floor etc. If your rogue still manages to get around all of that and get in a good backstab then I think they've earned it!
I love the idea that initiating a conversation from stealth could offer different conversation options.
Regarding AGX's concerns (which are legitimate despite the derisory tone) that the protagonist's voice is somewhat taken away with the party spokesman's idea, I tend to think that the party, as a whole, think as one (hence why you, the player, actually make the decisions in conversations). This does give me a cool idea though, that designating an NPC as the spokesperson might sometimes mean that you DON'T get the choice in what they say if there's a particular conversation option that they would definitely choose.
Finally it would also be nice to see as few "forgone conclusion" conversations as possible. I mean conversations that will always result in a fight no matter what. If that was the case then why did we talk in the first place? Some of the most irritating moments in CRPG have been conversations that take your PC rogue out of stealth, place them smack-bang in front of the half-blind half-orc fighter who would never have seen you, he then offers you a 1-2 line dialogue that basically says "me smash" and proceeds to pummel you into oblivion, all the while you're stood there thinking "how the f*** did he see me?"