So imagine that it's the ~*~future of gaming~*~ and you're playing a game like... Fallout or Alien: Isolation, (or another game I don't know because I don't play sneak games) and they integrated a function where, to sneak in the game, you must be quiet in real life. Would that add to the immersion for you, or would it just ruin it?

I think it would be hard. Especially if you have pets or roommates or something who might make noise, it could make it really difficult