I'm not so sure it's critical mass as much as it is we've been conditioned to accept the mobile+broadcast+timeline pattern as the primary form of communication. It's just everyone screeching into the void and wondering why they feel alone. Sorry if that sounds negative - I'm not trying to be... just attempting to put my finger on why people are desperate to reimplement the same patterns which have failed to provide meaningful dialog at scale on the major platforms. Popular opinion states if there were just more people on nostr, then people would engage in meaningful dialog, when I think the opposite would happen. Ephemeral broadcast does not engender meaningful connections.