I'm not sure the time and $$$ required to make BG3 a persistent world would be worth it for a few reasons. First, this game is set up in acts; as soon as you go to Act 2 you lose access to act 1 so the persistent world portion is over for Act 1. Not sure how much it would have really added to the game in a setup like this.
Don't get me wrong, if they had begun with having a persistent world in mind that would be different. I'm not opposed to it; I actually think it could elevate the game to a whole new game so I guess I'm just saying I don't think it would be financially beneficial at this point.
We are not talking about BG3 campaign being persistent. We are talking about a GM mode and the possibility to create persistent worlds with a toolset just like it was done in neverwinter nights.