With regard to the crate discoverability complaint, crates.rs (announced on this forum here) makes a good attempt at improving this in a highly performant way.
Adding a maintenance quality metric to the ranking algorithm would probably address the only complaint about the crate ecosystem that it does not already address. Something like checking that it compiles with latest stable compiler first. If it compiles then it is given a maintenance score of 1.0. If it does not compile with latest stable, score should be reduced according to date of last version update -- 0.9 if the last version was a month before the last compiler update, for instance, but 0.1 if the last version was two years ago. Use this score as a multiplier for the current "popularity" index.