Right now, systemd defaults to:
This is fine for most services. However, it doesn't work that nice for sockets where stdout needs to be be replaced with the socket. In that case, stderr defaults to inheriting the socket as well and needs to be replaced by syslog.
I think that if we're already defaulting to sending output to syslog, we could set DefaultStandardError=syslog as well. Then socket-services wouldn't need to explicitly set StandardError=syslog and could rely on the default instead.
More importantly, then user could just replace DefaultStandardOutput and DefaultStandardError in his/her config (i.e. with a logfile) and socket-services would tolerate that.