I don't think the fact that Rust is introducing features at a brisk pace, and the fact that people start writing libraries around them before they're released,

I don't think the fact that Rust is introducing features at a brisk pace, and the fact that people start writing libraries around them before they're released, have anything to do with whether Rust's backward and forward compatibility policies are good or bad. It seems unlikely, if Rust's policies do a good job of maintaining guarantees in a chaotic environment like that, that they would fail in a more placid environment.