Executives likely to use such a device aren’t using public transit.
Yes they are. Probably not in the country that calls it transit, mind. And lots of people would like to be able to have more private conversations in public, whether or not they’re travelling at the time.
Plus, I’ve seen a lot of threads over the years from gamers, or the people who have to live with them, looking for something exactly like this.
Cork insulation would usually be skimmed over with plaster. You could have a look at insulatiing plaster too, but I think that needs to be thicker than cork to work well. Less munchable by critters though.
In an old building, you need to use breathable insulation, breathable plaster, and breathable paint (and breathable mortar, if you’re repointing the outside). The moisture needs an escape route.