I may need to click through more, but isn't this inetd/xinetd?
I'm not sure what inetd/xinetd is, but the general idea behind websocketd is that you connect stdin/stdout of a process to a minimal websocket server. In doing so, you achieve UNIX-y composeability and a convenient network interface to an arbitrary process.
Right, inetd has been how you do that for like 30 years now. Any program with stdin and stdout becomes a network service that way.