phab:T154715 doesn't seem to be blocked on anything, so perhaps could be done before Friday. Then, it would highlight missing docblocks, which could be written.
Topic on Talk:MediaWiki Documentation Day 2017
Now that Codesniffer v0.8.0 is done, can we use it to identify the documentation holes in core, or is it still too buggy to apply there, e.g. not recognizing @inheritdoc.
There are some issues still, like @inheritdoc like you say, but there's a large number of legit CS violations that will now be highlighted. Fixing any is going to help some way towards getting core up to standard.
I'm not sure what the best approach is: I don't suppose anyone wants to end up with massive patches that do nothing but rejigg comments, because they'll be harder to read. But then, a huge number of tiny patches isn't good either, I guess? Perhaps one file or a small number of files at a time? Or one sniff violation? E.g. fix all "Missing parameter name" violations? Although that's likely to be huge too...
Either doing one sniff at a time or one class at a time would probably work.