> If you write code for 1.0 now, it'll compile on a future 1.0 release.

Almost: it will compile on all future Rust releases to the end of time (unless Rust wants to commit suicide). Languages cannot ever make breaking changes once they reach a stable version (unless they have relatively little adoption). This is even more crucial for "low level" languages like Rust, as they are often used for projects that are meant to last for decades, and are often chosen by programmers who want don't have the patience for this kind of thing.