There always be gaps in ownership and there will be some critical software left to individuals to keep the lights on. It's an ideal we need to move towards but we might never reach.
That being said, it really doesn't need to be this bad.
Here is a non-exhaustive list of critical tech currently in production without any maintainers:
- All of the authorization stack (2FA, Central Auth (otherwise known as SUL), authentication in mw, OAuth, etc.)
- All of the multimedia stack (from upload, to the video player, to the mw file backend, media handler, metadata extraction, etc.)
- FlaggedRevs aka Pending changes, a critical tool in the workflow of patrollers
- Abusefilter, the tool that prevents vandalism from being saved. I can't stress how important this is.
- SecurePoll, critical to community resilience.
- Deletion workflow
- Mailman (mailing lists), the very same infra that is sending and storing this email.
- User preferences
- Gadgets infra
- Beta cluster: The most important human testing infra before bugs hit production.
- SpamBlacklist/TitleBlacklist
You can go and check:
https://www.mediawiki.org/wiki/Developers/Maintainers and
https://phabricator.wikimedia.org/project/board/3144/query/open/ to see frustrations and open requests for years.
And even if a software would have an owner, it used to be that the team was under so much pressure to produce new things instead of maintenance that the software would practically be without a maintainer (or worse, as even volunteers couldn't unofficially take the role). I can example a few.