Maybe I'm weird but it doesn't really matter to me. I don't want to pick the Face as matter of min-maxing. I just want my character to be the "protagonist" even when there are better diplomats in my party.
+1 to this, and I definitely agree that whether or not anything else is changed, where the MC is present and not hidden they should be the default person NPCs speak to. (When it's essential that NPCs start the conversation at all.)
Perhaps totally revamping the dialogue system would be needed to have a true party feel to conversations, but I still wonder if something less than that would work as an approximation. You'd need to add a mechanism whereby more than one party member could be considered "in a conversation", either using the chain or switching to another party member as you can already and then having them click on the NPC or party member who are in the conversation to join in. But once that's added, then it surely wouldn't be that hard to make using the existing switch button able to cycle through party members who are now "in the conversation" and show the NPC's last line, but the responses available to the currently selected party member based on their race/class/background plus of course the common options but being able to use that character's skill points for checks. All that dialogue would need to be present anyway, given that all party members could conceivably be the only one meeting that NPC. And any party members not in the conversation could wander around and pick pockets as currently.
Or perhaps I'm missing an obvious flaw?