That we won't get a real D&D game and it will be up to the modders to fix the game to actually feel and play like a D&D game.
That's my greatest fear for BG3 at the moment. I have other worries as well, of course, but those are comparatively minor like hating most of the companions.
I don't think you know what D&D is, so let me explain.
D&D is a DM and players using a rather bad system based on what was popular 3000 years ago, now what makes it special is the DM and players, because the DM can do whatever he wants with the "rules" and the players engagement can make magic.
In a computer game you get one of those books with multiple choices, where a DM has unlimited choices, you may get multiplayer, but it's still lacking a DM, so choice limited and there is virtually no "roleplaying" to create the "magic", as everyone is locked into a story.
So what we have is a hopefully good visual novel with multiple choice mechanics, using a horrible (on computers) D&D system.