Is outbox more so the philosophy of: “reading from the relays others write to” If so, that makes sense. There are different ways to achieve that beyond NIP-65.

Relay hints can be useful for helping clients create a local database of where to find whom (aside from immediately loading notes you know nothing about), specially when you don't have any other clue about that, but NIP-65, NIP-05, nprofile hints, random guessing and historic event fetching stats, asking some smart indexing services and whatever else could also contribute.

Interesting approach, I had not considered using relay hints indirectly to infer where someone might be if you can't find their 10002.