From what I am reading, it seems Larian never really intended to be faithful to 5e. I believe their goal was to get the "feel" of D&D, not the actual ruleset. So that's what they are concentrating on: setting, races, story...etc.

And I'll chime in what I said awhile back. I think they dumped a huge amount of their budget on said graphics, art, cinematics to make the game look amazing. In that, they haven't failed. I think following the ruleset was a secondary thought and using a significant part of the budget for that was never a consideration. They figured they could just modify DOS with some tweaks and hoped it would resemble 5e. And that's what exactly happened. What they didn't expect was the old school BG players and tabletop players complaining. I think Larian wanted to cater to their audience (DOS) and probably thought the tweaks were good enough to satisfy the rest.

I am convinced we won't see any significant changes in combat. There will be some tweaks that can be done with the DOS engine but it will still feel like DOS with 5e adjustments and not the other way around. I think the announcement will discuss and emphasize the strengths of BG3, which is the cinematics, art, characters and possibly the story. And I think they will continue to say BG3 will have the "feel" of D&D but never really say it will be faithful to the current ruleset.