The premise of the plot doesn't seem implausible to me either. You've all been abducted by the Mindflayers, you've all got tadpoles. Sticking together will raise your chances of survival, so you stay even if you don't like each other. You can't have outsiders in the party – you can't keep the tadpoles a secret forever, and without the threat of their own tadpole hanging over their head, any outsider is liable to try to murder you because by all accounts you're a danger. Makes enough sense to me.
Really? There are plenty of folks in EA you can talk with that are perfectly friendly and helpful already. It stands to reason there will be more allies down the road. IMO the notion that 'can't have non tadpoled party members cause they'll cut our throats in our sleep' just doesn't hold any water. I mean, already we have Volo, Halsin and Wroot tagging along with the party-of course we *could* have non-tadpoled party members, and IIRC Larian is already planning that through the mercenaries mechanic as far as we know. Besides, Lae'zel already will literally try to cut our throats in our sleep and we can keep her around, so I don't see why this distinction of party members having to have tadpoles is a necessity.
As for the rest, It's one thing if it's an 11th hour party member in a jrpg, but the BG games...and BG III in particular have a lot of party conflict, with-as I mentioned earlier-lots of ways to lose party members. We are going to lose a lot of party member interaction when the cast gets culled at the end of Act I (even earlier if you side with the goblins) That party member interaction is going to be a lot less spicy and dynamic in act II if you only have 2-3 party members for the rest of the game.
BG II did it best with many party members tied to side content and quests. You get enough to get started and pick up the rest of your party as you adventure pretty organically, since there's a party member tied to a lot of the side quests and areas you'll be visiting anyways.
Most rpgs don't dump all your party members on your lap for the rest of a 100+ hour game within the first 20 minutes for good reason though, IMO.
