Even when I live with others, we aren't worried about bathroom noise.
I guess if you have a habit of talking to yourself while using the bathroom or showering and need to drown it out this is cool.
However, I'd love this as a general device. I get home and it auto plays music , etc
I think there's a specific target customer that would love this. I'm in the same camp you are... I couldn't care less. When it's just my wife and I at home it's pretty rare that we close the door even.
In university though I had a roommate who was absolutely paranoid about people hearing her in the bathroom. She would generally run the faucet the whole time she was in there to mask the sounds. Sometimes... I think she'd even run the shower; I don't know this for sure, but I'd hear the shower running in the bathroom for a while and she'd come out looking just as un-showered as she had when she went in.
You can do this with most home automation systems today.
As a seller it's none of your business what end users do with your device as long as it's not a safety hazard.