Doing something like that, just for the step forward in capability that mastering it would represent would be great, honestly, but it is a big jump that some studio would really have to dedicate themselves to. Fine hand animation work is still a big difficulty in big budget games, and there are ones currently handling it better than BG3, but if a game were to come out with something like that, that broke ground for advanced, intricate and complex hand animations that looked good, you're right - the knock on effect from someone managing that would be excellent for games everywhere.

In terms of D&D, and perhaps relevant here, the Drow use hand sign as a form of secret language - and pretty much all drow operatives you find anywhere who are part of drow military or espionage societal structure know it, and can speak it with others. It's not just a series of singular phrases or signals, but an actual full language, which is pretty neat. that's something we could even potentially come across in the future of the game.

Another interesting example is Nat, from Waterdeep Dragon Heist - Nat is an interesting case because she highlights a very real-world element of being someone who speaks with their hands; her sign language is self-taught and while being a fully composed language, it's one that is only shared by a very small circle of individuals who learned an developed it along with her. This reflects an often missed element of reality: you might communicate in a hand language, but when you go out, you know that 9 of 10, more, 49 of 50 even, people will not be able to understand you, even though you all share an language (and as an aside - this awareness leads to a practical pragmatism - if you speak with your hands, you generally carry a notepad and pen on your person wherever you go, because simply writing something down is often the quickest way to communicate). Aside from special services and community groups, your actual circle of people who CAN understand you is likely to be small and personal - people close in your life who have made the effort to learn, likely expressly for your sake, and that means a lot. Because it's personal, you might have a full formal understanding and use of a formal sing language (like Auslan), but your reality and day to day communications with this smaller circle of close people ends up developing a lot of short-hand and personal quirks that you have to filter out again when talking formally to someone you don't know, but who knows your hand sign. So, in Dragon Heist, Nat's hand sign is personal - and no amount of intelligent learned scholaring is going to let you understand it - but clever and wise people may be able to pick it up with on-going exposure to it.

All that said, this is kinda off topic, I think, so we probably shouldn't derail too far ^.^