A colleague flagged the availability of
$A.log (found in a blog) so we've spent a short while looking at it.
The links from e.g. How to use aura.log() and where does it print it output? now point to simple
console.log calls and there are posts here like LockerService not allowing subscribing to $A.logger. I don't see any official documentation on it (though Aura Documentation is dead right now so I can't check there).
Can anyone explain why it went away?