Took me way too long to land this, but it's real!
Detailed docs can be found here: Page Moved
You can now add github:org:team (e.g. github:rust-lang:owners) as an owner of a crate, and anyone that Github recognizes as a member of that team will get publish/yank rights. They will not get ownership management rights -- only named owners have this. In addition, you can only grant ownership to a team that you are already on (though there are no such restrictions for removing a team).
So now you can centralize ownership management of your 5000 single-function crates using your existing Github organizations! No more hunting down That One Person who actually owns the crate! You don't need to update Cargo at all to use this functionality, it's completely server-side on crates.io. However you will need to log back in to crates.io to provide permission to read your team memberships. Convincing Github that it's ok to read this info is a shockingly elaborate problem. If you're lucky, it will be painless (just like registering again). If you're unlucky, you may want to check out the troubleshooting info in the detailed docs.
If you don't want to provide this permission to crates.io, that's fine! Everything that worked before will still just work. You'll just get an error message any time you try to interact with the teams system.
Servo, rust-lang, and contain-rs have already kicked off turning this stuff on for their repos and everything seems to be working, but please let us know if you have any issues!