I don't have the app, but from what I've seen from some reviews of it, it seems that Clubhouse is only popular because there are interesting people interacting in it. That will be a problem to scale because, as we all know, the average human being is not that interesting. I can think of many apps that were like that in the beginning only to become something else afterwards (not necessarily being unsuccessful). The first that comes to my mind is Quora, that was a very interesting place in the beginning, but not so much today (but hey, still valuable!)