Yea, buy in and network effects are certainly the tricky part. But that’s also true of the fediverse … it’s been going a long time and in many ways was really “gifted” with Musk’s twitter purchase (seriously, if someone else were to take charge there and reset it back to pre-musk, you’d see a bunch of people leave masto) … and Spez’s API pricing. Before these events, the fedi was pretty quiet compared to now. Lemmy, before the reddit migration was very quiet and may very well have failed by now or soon were it not for the migration.

Moreover, ActivityPub doesn’t get you seamless network effects. Lemmy and mastodon mostly don’t have cross-traffic, and that’s because their platforms basically lack any mutual support for each other. If they worked well with each other, Lemmy would be a much busier place (and masto would be better structured). Same probably goes to some extent for things like Peertube and bookwyrm. There’s also the lowest common denominator effect when it comes to features. One platform may support/provide “Quote posts”. But because Mastodon doesn’t, and they have the bigger user base, it doesn’t really matter, as no one else will see the quote posts and so the new platform doesn’t really have much to offer new users, which in turn basically turns the fediverse into the mastoverse (which is actually happening) and undermines the promise of enabling new platforms with built in network effects. Mastodon could just become one big single server or platform today and many probably wouldn’t mind.

Otherwise, RE SSO, I had in mind that trusted platforms would be mutual sources of authentication such that an account on one is effectively an account on all of them.