A self-describing format seems important here. If the binary payload has no version or algorithm identifier, but the human-readable ALG/KDF/ENC lines are ignored by decoders, how would a wallet reliably distinguish future profiles or reject a mismatched wrapper?
It may also be worth defining the recovery UX as part of the interoperability requirements: checksum or typo detection before running the KDF, an explicit wrong-password result, and test vectors covering corrupted backups. For long-lived paper backups, reliable failure behavior may matter as much as keeping the encoding compact.
Is the fixed 104-character requirement providing a concrete scanning or transcription advantage that would outweigh putting versioning inside the authenticated payload?