Changes to the LogHandler API require dance around creating new overloads, deprecating old overloads, which unnecessary bloats LogHandler protocol surface (like happened with the source: parameter). We have upcoming changes that would introduce new capabilities to the LogHandler protocol, for example https://forums.swift.org/t/proposal-slg-0003-standardized-error-metadata-via-logger-convenience/84518/35. It makes sense to introduce a single container structure for all the data associated with a log event before introducing any new overloads in LogHandler protocol.