TLS certificates are not just used for web stuff either, many protocols use TLS. For example in IoT world, MQTT over TLS is common. One non-TLS-based protocol

TLS certificates are not just used for web stuff either, many protocols use TLS. For example in IoT world, MQTT over TLS is common. One non-TLS-based protocol I can think of is SSH, and I agree that SSHFP does sound useful. But given the limited use case of this, SSH's native certificate support, and how easy it is to pre-fill the known_hosts file, I don't think this feature is worth implementing DNSSEC.