@Gargron I just found out about PeerTube that's compatible with Mastodon, and I'm thinking ActivityPub could be a killer feature for federated platforms.
Closed platforms like FaceBook and Twitter actively work to prevent users from sharing media between them.
Meanwhile, embracing integration is a huge benefit from user perspective, as it means you can primarily use your platform of choice, but you can still interact with the users of other platforms.