I find the total lack of mw.log usage surprising. I suspect the reason may be that it takes up space/bandwidth, which - given that it is a no-op in production mode - is understandable.
Enabling logging output in PHP gives one a useful trace of the general process from initialization to handling of the request, building response, etc..
Perhaps we can find a way to filter them out in production mode? (Either in minification or some post-processor.)
 Not an MWHook, as it's a standalone library. But this may work: