As far as I can tell a lot of the changes seem to be matching what Wizards of the Coast are doing with the next generation of D&D releasing next year. So it seems to me like WotC are likely involved in some capacity in how the rules are handled when deviating from 5e and I very strongly suspect they want BG3 to reflect as much of the next gen player handbook as possible. The problem I have there is I have no faith in what WotC are doing as some of the early changes they proposed were catastrophically bad and worse they want to say the next generation of D&D is backwards compatible with 5e...they're not even willing to leave 5e alone. The next gen rules are still being tinkered with all the time and BG3 launches in the middle of that so it will probably end up in a weird limbo where the final product is neither 5e nor 6e.
Just a point here: WotC isn't working on a 6e. It's working in a 5.5e. Everything will be compatible to 5e material exactly in the same way 3.5 material were compatible with 3.0 material. Nothing new on this front. They said that this edition (5.5e is unofficial and oned&d has been scrapped) will be their last and will live in perpetuity but this is just laughable. By 2030 I bet there will be a 6th edition.
