Can you explain what you mean by outbox model?
i think it just will take a little more pushing at the guys in client dev most likely to get it working - nostr:npub1jlrs53pkdfjnts29kveljul2sm0actt6n8dxrrzqcersttvcuv3qdjynqn and nostr:npub1ye5ptcxfyyxl5vjvdjar2ua3f0hynkjzpx552mu5snj3qmx5pzjscpknpr
in fact hodlbod is further ahead at getting NIP-42 working, and he is also the most advanced on markets, but nostrudel has got outbox model working which is also critical because relay development needs to not be a black box,
nostr:npub180cvv07tjdrrgpa0j7j7tmnyl2yr6yr7l8j4s3evf6u64th6gkwsyjh6w6 has contributed in a big way with building the khatru framework to make it easier for relays to be built, and i've worked on making proper CLI interfaces using direct messaging and cleaning up the organisation of his nostr library so it is more easy to understand, and fixing several concurrency bugs and improving the json processing
Discussion
https://github.com/nostr-protocol/nips/blob/master/65.md
mostly this... it enhances the old relay list by specifying which ones you read from and which ones you write to
the outbox model means pulling this event type and using those for the relevant case, so, posting to where you read, and reading from where you post