Right - the bulk of the article is about how the “cool factor” of scarcity and variable rewards induce a demand greater than what might be there if they were simply wide open.
So two things: first, they are opening the app up to anyone (and on Android) in the near future (timing TBC of course). It'll be interesting to see if the hype they've built will last all the way through to then.
Second, I fully agree with you that opening the app up is actually problematic for them. It's almost like the opposite of the network effect, where I think having more people on the platform is going to potentially make the quality deteriorate. Right now, it feels authentic but somewhat curated (i.e. we have moderators who invite high-profile and very interesting panelists on to speak) - I'm not sure that will be maintained when it becomes a free-for-all.