Thanks for posting this Ruben, very interesting :).
the first app to sculpt documents and containers in your pod determines where other apps need to look for data.
I agree that this is what’s happening in practice today, but I don’t think that’s the idea of Solid. Ideally, apps should be using the Type Index (or Solid Application Interoperability, etc.). But they don’t, so I think the problem is that most apps are not following best practices, not that this is how Solid is supposed to work.
I see two ways to solve that. The first one is to actually enforce them, but I worry that it would increase the barrier of entry for new developers. The second one is to make it so trivially easy to use that everyone does it; either because it’s a well-documented best practice or because most libraries in the ecosystem do it out of the box.
And maybe the second one would be the best approach. I like to think of this like how lenient HTML is with mistakes. You can write HTML that is not 100% valid, but the browser will still render it, instead of throwing an error. In that regard, I think it would be fine if 90% of Solid Apps used the Type Index but not all of them. The problem is that at the moment, almost none are using it.
This seriously hinders interoperability and serendipitous reuse, which I consider absolutely vital to a thriving personal data ecosystem.
I agree with this 100% :D. I wrote a post a while ago titled Interoperable Serendipity, and for me this is THE point of Solid.
Implementing graph-centric pods and views
My opinion of graph-centric pods is that they sound great in theory, but I worry that this will never happen in practice :/. I’ve been developing Solid Apps for 4 years now, and I’m still missing things as simple as paginating data.
Sure, I’m saying that from an impatient app developer’s point of view; I understand that things take time. But honestly, I’d much rather have a document-centric Solid POD that works in practice, than being caught up in theoretical discussions that never become a reality.
As an app developer, I also had this question of where I should place the data. But ever since I learned about the Type Index, I don’t have it any more. And even though it’s not perfect, it gets the job done for many use cases. Still, nobody is using it because it’s still a draft and it seems we’re waiting for the perfect solution before settling on anything.
As you mention in the article, a graph-centric POD is backwards compatible with a document-centric POD. So I think at this point it’s more useful to develop the existing document-centric architecture further, and transition it towards a graph-centric architecture eventually.
In any case, I’m just a mere app developer and I haven’t thought deeply about these topics, so I may be missing something for sure 
. But my impression is that such a paradigm shift would slow down the progress of Solid even more than it already is.