Maybe, maybe not, but even then, wouldn’t implementing those be easier (for both you and the rest of the world) than creating a completely new protocol?

> It still leaves the issue of it using multiple ports.

Aren’t multiple ports only an “issue” if you assume NAT (and CGNAT, shudder) as a natural state of things?

Maybe. One the other hand, WebDav and SFTP may be more widely supported than those extensions already.

>Aren’t multiple ports only an “issue” if you assume NAT (and CGNAT, shudder) as a natural state of things?

NAT is unfortunately something ubiquitous. And the multiple ports makes FTP harder to tunnel.