NaCl addresses a different problem than OpenSSL. NaCl is great if you have no legacy or compatibility requirements, and it should be the only crypto library most web and mobile developers ever come within a mile of. But it's not a workable replacement for OpenSSL.

For per packet encryption.

For authentication, there is CurveCP.

People seem confident with OpenSSH's authentication mechanism. Why not use that?

At some point one has to trust that the IP address one is sending/retrieving data to/from is the correct one. That's easier said than done if some host wants to keep changing its IP address every few days.

The SSL PKI scheme (the SSL approach to authentication), as implemented for public websites, is not much of a confidence-builder, IMO. Opinions may differ.

If websites maintained consistent IP addresses and we could authenticate these machines using OpenSSH keys, I would be more willing to believe we could verify their "authenticity".