Do you need a blockchain for that though? There are cryptography schemes to share a secret (e.g. the recovery keys) between multiple parties, requiring at least N of them to get together to recover the original value of the secret.
No, but you need some sort of blockchain to enforce uniqueness in petname systems due to zooko's trilemma.
If you're okay with another side of the triangle, where all of the identities are keypairs, then you don't need a petname system or any name system. the name system is an optional convenience layer on top of the web of trust.
