Truthfully I don't even think simply changing the character that is speaking goes far enough. Nor, indeed, should it be as simple as 'just add all bonuses to whoever is speaking, regardless of stats'. Either of those is perhaps fine for solo player, but in the case of co-op it becomes unwieldly. I'd much rather see a SWTOR-like system, where every dialogue choice is a vote, and then whichever wins is spoken by the character that voted for it. This is a MUCH more natural form of dialogue that involves all of the characters, and doesn't leave anyone feeling left out. It also encourages some different skill spreads.
The current system, regardless, is not a good one. It was a problem in DOS2. It technically worked, but it was incredibly annoying and we were forever reloading and trying to get the persuasion character to be the 'talking' one whenever it was relevant. DOS2 didn't have a TON of these, so it was mostly a problem with 'forced' dialogue cutscenes after bosses or walking into an area. BG3 is liable to have MANY more skill checks, however, and we shouldn't feel the need to simply have one person do a lot of the talking or constantly save scum.
Sure, D&D often has a 'face'. But some things are better enhanced by the medium we're playing in when the options are there, and a SWTOR-like system would do it.
I'm not opposed to an even more sophisticated system but in my mind it should be relatively easy to implement the possibility of the PC taking over the conversation from an NPC yet for some reason that option has not been in DOS2 or BG3 EA eventhough it was requested from the start. Since I can't know what I don't know I'm just gonna assume there are some problems in changing the current dialogue system and I would expect a completley different system would be even harder and more expensive to implement than "just" changing which character is talking, thus I proposed the simplest alternative I could think of that would (mostly) solve the issues I mentioned in the OP. Just adding the bonuses would only work if all the other possible tags would also show (so the options for both druid & Fighter show, if both are in the conversation and would have different options). As for MP: true there could be some issues but for all I care they could always let the "new" character take over. I expect PCs in MP to cooperate so I wouldn't expect any major problems from that point.
An argument I forgot to mention in my OP: Even if consistency issues would appear by a sudden change of who is talking (assuming no additional reqording of voice acting or changes in animations etc.) I can't imagen those beeing any bigger than the current status quo.
