Here's a related bug I filed back in 2008 about using wfDebugLog instead of wfDebug so that a system admin can determine more easily where log messages are coming from. https://bugzilla.wikimedia.org/show_bug.cgi?id=14601. Something to think about.
Topic on Talk:Requests for comment/Structured logging
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Thanks for pointing this out. I've added it to the "See also" section of the RFC.
And since Dec 2012 ( https://gerrit.wikimedia.org/r/37442 ) the log bucket is prepended to the message when it falls in the main $wgDebugLogFile. So we could potentially replace all the wfDebug() calls right now, though having wfDebugLog( 'default', 'some message' ); is not idea.