Bg3 is going to be a videogame and Larian already made their choice about the combat mechanics, and they are working on it. Logically, It is going to be a videogame based in D&D 5e so no one expects that playing bg3 is going to be exactly like playing a D&D tabletop game with your friends because those are very different platforms. One will be a video game, the other is a social adventure simulation tabletop game. And surely Larian´s goal is to make a good videogame, not a perfect simulation; and Sven Vincke already stated that some rules are going to be bend (because, as I said before, they are making a videogame and you have to adapt things, cut others; the same as in the videogame adaptation of VTMB 1&2: they will never use "mask of a thousand faces" for lots of practical reasons, for example).
But if someone will want to do the most faithful representation of a D&D 5e ruleset in a videogame will find it difficult to do it in real-time, even in real-time with pause, because of the nature of some of the mechanics of 5e. Anyone with a minimum experience in the tabletop will surely see some of the problems. There are plenty of reasons already stated in this thread so I do not think to repeat them is needed.