Could Passkeys ever be used for SSH? I purchased a Yubikey to use as an ed25519-sk key but found the implementation to be too drastic of a change to my workflow to be comfortable with. TouchID / FaceID for SSH would be a totally palatable solution however.

Interesting question. Though, if you don't specifically need syncing, there are already apps for storing SSH keys in the Secure Enclave, such as Secretive:

https://github.com/maxgoedjen/secretive