Not only that, the registry key would be reserved for using an alternative front-end registry.
crates.io, the default registry, would become a caching proxy for the other registries. so every time you make a crate using, say,
email@example.com, rather than fetching directly from
mozilla.org, it would fetch through the default registry.
Crates on the default registry wouldn’t need the
It’s also better to have active registries, that push to federating registries. Otherwise, if you had say 100 or 1000 registries, they’d be regularly hammering your registry for crate updates.
Do take a look at mastodon / ActivityPub. It’ll probably help to clear things up. (note that Activitypub Over Static Pages (AOSP) isn’t really a thing. also note that AP allows both the caching and the backing servers to block eachother, so for things like proprietary no-redistribute registries, they can simply block federation.)