In this interview, in 7.40 the interviewer asked Swen Vinke about the origins stories in DoS2 and if they will make a comeback in bg3.
https://www.youtube.com/watch?v=M57vTyM-iE4Swen answered that It´s a system that will evolve. One of the things that they focus on is the party and personal stories. It was explored [in DoS2] but it was not really explored as I would have wanted. Party will be important but also the Hero
[singular] . In this party, each Hero has the story of their origin if you choose that but you can also obviously make your story anyway.