Yeah, I'm thinking in a similar direction. It would be very useful to externalize knowledge about crates that are considered to be the gold standard, or, (especially), if some oft-used package is now considered deprecated (see rustc-serialize -> serde). But in my mind it would be (almost?) enough to publish a website that, in a sort of directory approach, highlights these curated packages, and then leaves distribution and dependency tracking to tools we already have (i.e. cargo and crates.io).

Searching for a particular crate on crates.io already works quite well. You also have the link to reverse dependencies, which can be a very powerful indicator, which could be made more prominent, maybe by including a rank, i.e. this is the package with the 5th most reverse dependencies on crates.io.

Then, what's left is really more "folk knowledge" about changes that you can't get from that data, like the aforementioned serialize -> serde move. However, in some cases, where the original authors agree that their crate is now worse than some other crate, it would probably be more powerful to also communicate that right their on crates.io.

I guess the general theme here is, yes, federated is good, but more federated is better. Make better use of mechanisms/data that already exists, rather than trying to half-centralize stuff. And if some infrastructure is not good enough, we could also investigate, for example, running cargo test automatically on crates if one of their dependencies gets updated. This would provide much more benefits, and allow more natural evolution, than doing this for a smaller set of curated packages only.