[rakoo]

AP, even in its purest simplest form, already allows to "revive" and "remix" data: you have the JSON of the data, you can do whatever you want with it. You can build a product injecting JSON of this data, just like in AT, but those product don't really exist so even if I can say "yes you can fork them" it's all talk.

There's no talk about migration in the core spec, but how is it in ATproto in practice ? Does everyone carry their entire repository, live from their own PDS, ready to be remigrated somewhere else ? It does feel like in AT-in-practice people just have a PDS and that's it ? (I've never used it, I might be totally wrong)

Really, if you want a simplistic view of AP, it's easy: it's an INBOX where you receive content, and an OUTBOX where you send content, and the content is activitystreams-formatted JSON. Anything else just makes it easier to work with.