I doubt this 7 days to get the tadpole out is going to be the entire game. I'm sure there will be a lot more story after that, so maybe there will be a more solid connection to BG1/2 rather than just references. Maybe the events of the earlier games are somehow responsible for this illithid uprising? I'm not saying this will be the case, but we don't actually know much of the story so I don't think we can say it has absolutely nothing to do with BG1/2 yet.
Also BG2 was pretty good at closing up the story line so I'm not sure what a true BG3 could do that wouldn't seem cheesy or anything.
