If the note signature (by the author) were to include the latest Bitcoin block hash that would work as a proof of time (the earliest).
Just by using regular RSS-feed bridges from the regular Internet source to Nostr accounts a lot of the current sources could be verified to be tamper-proof (OG/modified) better than now.
Combine that with the hash of the article and this becomes even more interesting for posteriority. Could be combined with archive.org/.today storage.
nostr:npub1t89vhkp66hz54kga4n635jwqdc977uc2crnuyddx7maznwfrpupqwra5h9