It would be nice if zabbix agent had the ability to check if a unix domain socket exists, that it is in a listen() state and is accepting connections.
Monitoring Unix Domain sockets can only be checked on the local machine, so having this check built into the zabbix agent would be very convenient.

Example:
socket.listen[/var/run/socket.sock] would check the /var/run/socket.sock exists and is in LISTEN state (similarly to existing agent's TCP port check net.tcp.listen[port])

socket.connect[/var/run/socket.sock] would check if it's possible to connect to /var/run/socket.sock (similarly to existing agent's TCP check net.tcp.port[<ip>,port])