As a player who enjoys playing with a friend I've had a lot of fun with the Early Access so far. One of the points that has bugged me the most, however, is how the dialogue works. I'm not talking only about the dialogue between the two player characters, which I believe is definitely an Early Access problem (half the time I can't tell which of the PCs are speaking, nor what dialogue option my friend chose), but of the actual dialogue between PCs and NPCs. I think the current system, where the player who's not doing the speaking is basically a passive observer, being able to make suggestions is definitely not enough, in my opinion. What I suggest to address this issue, although more ideas are always welcome, is to use a similar system to Star Wars: The Old Republic, where both players can choose a dialogue option and it affects their alignment (for BG 3 I think this could translate into the opinion your companions have of you). Another feature of this system is deciding which of the PCs actually get to choose the dialogue option with a throw of the die. Although I don't think this second feature is ideal, it is definitely better than the current system, where the player who initiates dialogue makes all the decisions.
In sum: Multiplayer dialogue needs to be more engaging for both players, not just whoever initiates the dialogue. All players should be able to influence their companions' opinions, if participating in the same dialogue, at the bare minimum.