Was just listening to the latest episode of Dot Social podcast where there was a discussion with CEO of Ghost (alternative to Substack). They're integrating ActivityPub into the platform, but where they're going with it is that you can use your Fediverse ID instead of email to sign up.
Once they have that worked out, any likes or comments automatically migrate back to the fediverse. Replies back to replies also show up in your timeline and your followers can see them. This makes discovery pretty effortless. They can also use the stats to keep track of engagement across all fediverse services.
It also means turning one-way streams like RSS (podcasting), email services, and commenting services into common two-way communities.
You're now going beyond just catching up to existing services and doing things just not possible in closed silos. Real "Aha!" moment.