In their chosen example, and many others that involves external sources, it's not really "your" data, though. You have no control over the structure, and you then have the choice of deciding whether you want to throw away what you can't shoehorn into your current schema, or store it and transform it as best you can and be prepared to re-transform it as your system evolves.
Really, they're not avoiding modelling the data. They're modelling it in their "P-stores" whether they want to admit that's just another data model or not. It's clearly not data models they object to, but typical database DDL coupled with a desired to not throw away data that doesn't conform right now. Depending on your application domain, not throwing away data that doesn't conform to your current data model can be good or bad, but it's not an accident that they picked Twitter/Mastodon where it's easy to justify not rejecting non-conforming documents.
I agree with you that this doesn't require ditching relational models, though. For that matter not even SQL. You can even fairly easily build this kind of architecture without e.g. ever leaving Postgres (replicated pair for their "depots"; triggers + postgres foreign data wrappers to materialize views on index servers and/or to do requests across index servers).
Really, they're not avoiding modelling the data. They're modelling it in their "P-stores" whether they want to admit that's just another data model or not. It's clearly not data models they object to, but typical database DDL coupled with a desired to not throw away data that doesn't conform right now. Depending on your application domain, not throwing away data that doesn't conform to your current data model can be good or bad, but it's not an accident that they picked Twitter/Mastodon where it's easy to justify not rejecting non-conforming documents.
I agree with you that this doesn't require ditching relational models, though. For that matter not even SQL. You can even fairly easily build this kind of architecture without e.g. ever leaving Postgres (replicated pair for their "depots"; triggers + postgres foreign data wrappers to materialize views on index servers and/or to do requests across index servers).