I'm planning to refactor logging so it's all done through a single function. I'd be happy to look at logging to disk as well (customisable?), but I'm against integrating directly with anything on the OS or a third party service.
I think the best option is to use PHP's (error) log functionality for disk logs as these logs will be outside the web root directory & automatically managed by logrotate. There are many services that will ingest/stream file system logs for viewing elsewhere (I think AWS and Azure offer native agents for this), or you could point the PHP logs to syslog and ship them off somewhere with rsyslog.
Thoughts?