Unlike other languages that are "done" at 1.0, Rust will still be improving and iterating. 1.0 defines a backwards-compatible release that you can depend on but the language won't be "done".
"It’s important to be clear about what we mean by stable. We don’t mean that Rust will stop evolving. We will release new versions of Rust on a regular, frequent basis, and we hope that people will upgrade just as regularly. But for that to happen, those upgrades need to be painless." [0]