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.
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.