The minute that relays start charging users, many people will just stop using that relay. And a dev will launch a new piece of software that will bring up a new relay on a smartphone, and it will get a million downloads.  (Please...)

What is keeping people from joining is the fact that all of their friends are still with them in the corporate algorithm advertising cage. We need to just keep talking about Nostr and making it a place that people want to be.  The rest of it will be history.