Every Bitcoin private key generated this decade can be written down on a steel plate that survives fire and flood, but Nostr keys still live mostly in password managers and iCloud screenshots. The math to bring the same physical-backup workflow to Nostr has been sitting in every Bitcoin library since 2013, hiding inside a step of BIP39 that the NIP-06 flow happens to skip past. Below is the case for a backwards-compatible 24-word encoding of any existing nsec, the cryptographic reason it cannot collide with a Bitcoin seed, and the NIP that needs writing.