> relaying auth requests to your phone for approval and storing secrets in the Secure Enclave

Like the acquired/abandoned https://github.com/kryptco/kr [key stored in a [...] mobile app] with iOS and Android apps all under an "All Rights Reserved"-source license?

Also, newer Macs have a Secure Enclave (supports 256-bit secp256r1 ECC keys):

https://github.com/maxgoedjen/secretive [storing and managing SSH keys in the Secure Enclave [...] or a Smart Card (such as a YubiKey)]

https://github.com/sekey/sekey [Use Touch ID / Secure Enclave for SSH Authentication!]