I'm generallt in favor of alignment as a thing that exists to help guide character creation. Especially for less experienced players in both video games and tabletop, it can be nice to have alignment to fall back on as a sort of 'when in doubt' option. That being said I think this would be a bad idea to implement in BG3 for two reasons.
The first is that I don't think BG3 really needs hard alignment in a story sense. I don't think that having alignment would improve the delivery of the story or its themes. I will insist that Wrath of the Righteous needed alignment because the whole point of the game is about becoming an extra-planar being, something that's more and less than human, and thus is more primal, more elemental, more ruled by these otherworldly ideals.
The second, bigger reason is that I don't for a moment think Larian's writers could actually do it well. I don't think they could present those choices with the nuance and consideration such a thing would require. Even WotR fumbled the ball at several points and I think their writing is overall superior. Larian demonstrably doesn't seem to prioritize giving our player characters nuance in their choices.
