There was a good discussion online between Christine Lemmer-Webber, one of the editors of the ActivityPub W3C Standard, and Bryan Newbold, protocol engineer at BlueSky.
- CLW - How Decentralized is BlueSky Really?
- BN - Reply on Bluesky and Decentralization
- CLW - Re: Re: BlueSky and Decentralization
These are long reads. But they are worth reading. Christine and Bryan agree that ATProto and ActivityPub have different design goals and so what you get from “federation” with each is different. ATProto makes a centralized index of the entire system possible, at the cost of relying on very few (practically likely one) centralized providers.
As a result, the Lemmy ecosystem, as it exists today, wouldn’t be possible with ATProto. It would probably look more like Reddit, but with a “credible exit” possible as a defense against enshittification.
For those who don’t know, Bluesky isn’t really federated. The only way to host a non-Bluesky instance required 1TB of storage in July 2024, and 5 TB of storage in Nov 2024. Could be way more than that now.
You basically have to be a company to federate into the ATProto (Bluesky) ecosystem. You can’t just “stand up an instance”.
Lots of detail: https://dustycloud.org/blog/how-decentralized-is-bluesky/
(I know you’ve already realized that you were conflating Mastodon with Bluesky, I’m putting this here for others who come along so they can get the facts).