Default settings in clients are a huge piece of this. Doesn't matter how decentralize-able nostr is if clients push users toward centralization. I for sure see the benefit of outbox enabling clients to find where a note exists, but I don't think it's a silver bullet. I'm really curious about the gaps it leaves in user experience. Not everything works well in a decentralized manner. Search and discovery is one of the first ones that comes to mind.