Hey Robert,
HSL in an iRule is definitely an approach that would work on a per-iApp basis. The goal here is to achieve Connection Logging globally for all traffic, so we maintain proper Security policy without running the risk of forgetting to configure logging on certain iApps.
We have also setup a template that configures this for all of our HTTP iApps but still there will be other custom implementations that would allow for mis-configuration and skipping the iRule. We would like to assure that all connections are always being logged.
Thanks