It is really great how they write "TLS use cases" and in fact mean HTTPS use cases.

CA/Browser Forum has disallowed the issuance of server certificates that make use of the SRVName [0] subjectAltName type, which obviously was a server use case, and I guess the only reason why we still are allowed to use the Web PKI for SMTP is that both operate on the server hostname and it's not technically possible to limit the protocol.

It would be perfectly fine to let CAs issue certificates for non-Web use-cases with a different set of requirements, without the hassle of maintaining and distributing multiple Roots, but CA/BF deliberately chose not to.

[0] https://community.letsencrypt.org/t/srvname-and-xmppaddr-sup...