Then you'll enjoy reading about the nosh toolset and s6-networking, which both separate the listen-accept model into separate programs and have the ability to invoke "wait" servers with the listening socket.
It has one terrifying disadvantage. The socket is opened and appears to be owned by pid 1.
I haven't seen the code that does this, but my hope is that it is perfect in every way - if not then its an open door from the internet into my server.
This can work for simple services like sshd which fork for each connection anyway, but would never work for something like nginx or redis.