The problem with building a closed social network is that it sets up an all or nothing premise for users. They might like some of the signature features but they'll leave if there's not enough people to network with. That's a shame and a huge barrier to innovation and new social products.
The #fediverse changes that forever. People can now use the features they like from a mix of apps across a common network of people. This means we can take a whole new approach to how "social" and "media" should work including discovery, user experience and monetization that will be far healthier than anything we've had in the past.
