How do you see argo tunnel fit in this scope? It obviously has other features (cert management, internal routing) - but you'd have to keep competing against http standards with your protocol, no?
Argo Tunnel does a specific thing: make a connection from a client's server to Cloudflare (rather than the other way around). This is helpful from a scaling perspective (why have a load balancer when we can do it?) and a security perspective (no open ports). If there was a standard that did the same thing as Argo Tunnel we'd adopt it.
We actually use standard protocols for the Argo Tunnel connection and we'd look at HTTP/3 as a possible mechanism for it. I agree that if there's a persistent connection the benefits of QUIC (and HTTP/2) are lessened compared to a browser doing a drive by on a web site. This is one reason the OP above is wrong about Cloudflare, HTTP/2 and Railgun.