Apologies, I'd implied that we have multiple s6-supervise processes running and their children pipe to one file which is read by one s6-log file.
You can achieve this outcome by using s6-rc's, where one consumer can receive multiple inputs from producers. There is a special (but not unique) case where a program, such as apache which will have explicit log files (defined in apache's config file) to record web-page accesses and error logs, on a per server basis. Because all the supervised apache instances can write to one error logfile, I instructed apache to write to a pipe. Multiple supervised apache instances using the one pipe (aka funnel), which was read by one s6-log. This way reducing the number of (s6-log) processes. I could do the same with the access logs and use the regex function of s6-log, but I tend to simplicity.
