I think it would be amusing and practical if other people can knock on your room door letting you know that they're out there or they want to come in. Doesn't mean you have to let them in though
People can already knock on doors but the players inside can't hear them. Something even cooler would be to add peepholes so you can take a gander at who's out front. I imagine this would come in useful for people who don't want their places raided.