The most recent developer satisfaction survey supports the claim that
volunteers find it hard to get code reviews. The hypothesis is that by
having clearer ownership around code, there should be clearer
accountability, and it should be clearer what code lacks ownership that
This also applies to Wikimedia staff. It's often not clear when needing to
make changes to core, who is the best person to talk to about that code,
and who should be responsible/accountable/consulted/informed about any
changes to the code.
I am involved in the development of the Desktop improvements project 
and when we began the work there was no recognized owner for a lot of the
skin code in core. Since then my team has taken the role of maintainer and
it has allowed us to drive a lot of changes. I'm seeing new skins pop up
and we have started hearing from skin engineers, so I feel this has been a
positive thing. However, as we've navigated other parts of the codebase,
we've had to ask a lot of questions such as "Who maintains the legacy
parser? Are they open to changes there, or should that code be considered
of the watchstar?"
What with the proposed move to Gitlab, I have been very interested in the
code owners file documented on their site 
I hypothesize that identifying code owners and getting Wikimedia
engineering to agree to some basic expectations around code ownership might
go a long way to helping set expectations around who to talk to about
making changes, and actually getting those changes carried to completion.
The experiment of adding an OWNERS file to MediaWiki core seems like a
cheap one, given if we find it does nothing the file can easily be removed.
If you are interested in helping me explore this, feel free to join the
conversation on https://gerrit.wikimedia.org/r/c/mediawiki/core/+/745946
Wishing everyone a happy holiday