Seems like the perfect thing for me (I run a stupid dual-traefik setup that does TLS SNI negotiation for me that I want to get rid of), but I can't figure out what is this.
mDNS is just the method of communicating what traffic should be sent where. The "switchboard" listens for mDNS broadcasts that tell it what services want traffic routed to them under what conditions. A "node" (which was a bad choice of words) is the other side of that, a program broadcasting one of those mDNS resources (e.g. send traffic that's been sent to the domain "example.test" to this machine on port 8080)