Honestly my guess is that the only way any of the decentralized/federated social media protocols are going to massively grow is with their adoption on larger more corporate platforms. Not a lot of non-nerdy people seem interested in managing cryptographic keys or searching out Activity Pub instances, but Threads managed to get ~200x the size of Mastodon and even BlueSky managed to get ~6 million users in like a month.

Now of course if there's a lot more people on big corporate platforms that can communicate with anybody on Nostr/Activity-Pub/AT then there'll probably be more people who'd be interested in migrating away from the big platforms to the more decentralized/federated side of things. But I doubt a large percentage of microblogging users will ever be outside of larger easy to join corporate platforms.

If I turn out to be right it's not all that bad IMO. I can talk to fellow nerds here on Nostr as well as communicate with those on Threads, BlueSky, other future big platforms, and all of the fediverse from within my Nostr account here. My 2c anyway.