I've analyzed how dependencies change over time. Specifically, I note when crates change their dependencies, and stop using some of them. This lets me graph dependency additions and removals over time.
I've used this data to make a chart of "active" reverse dependencies over time. By active I mean crates when they use a given dependency, and haven't removed it (yet) in a later release. Additionally crates stop being counted as actively using a dependency when they appear to be abandoned themselves.
For crates that are dead, this gives an armadillo-shaped charts! Here's the gcc crate (red is when it's losing popularity):
and here's one for rustc-serialize:
and here's serde doing well:
I'm very happy how clear this data turned out. Download numbers don't show these trends clearly, e.g. the obsolete
gcc crate has still 130K downloads per month! The
cc replacement has 6 times more downloads now, but 57 times more active reverse dependencies.