There is no good reason, but from what I understood while reading sources, SIGHUP will cause s6-log to read last lines and execute log script, so that might be useful.
It's also the case with SIGTERM. Unless the -p option is given, which you shouldn't use (it's a special option only used for the catch-all logger to make sure it doesn't die when the system gets shut down). SIGTERM is generally the correct signal to use to stop a long-lived process.
Also, have you considered combining = action and ! processor? Not only to store matching log records, but also post-process them? For example, if you see some periodic information let's say current temperature, this way you can extract log line with that temperature, and store just the numeric value in a file.
There are lots of things that can be considered. I try to add as few features as possible, because doing otherwise is a surefire way to explode complexity. Having an idea and a theoretical example isn't close to compelling enough to clear the bar of "yes let's add this!". If you can come up with two real-life examples where the feature would be a significant improvement, where it makes a thing possible when it previously wasn't (or was significantly harder), then it's worth revisiting. -- Laurent
