I never actually considered the idea that established websites implementing activitypub to join the fediverse would be an important part of its growth. This is fascinating!
I’ve been talking for a while about how the fediverse might dethrone youtube - which is maybe the biggest challenge it faces - to become the default form that people use to consume content, but I’ve only ever thought about it in terms of collapse and replacement. I don’t see youtube implementing activitypub any time soon, but maybe if more sites fo it and it becomes a key selling point that might start to tip the balance more.