As an addendum, there's nothing preventing anyone from packaging multiple versions of Rust assuming it properly supports it (for example installing to /usr/bin

As an addendum, there's nothing preventing anyone from packaging multiple versions of Rust assuming it properly supports it (for example installing to /usr/bin as rustc1.10, then we can symlink /usr/bin/rustc to the most recent one) - and if Rust releases a 2.0 at some point it is likely that there will be multiple versions available for a release or two while programs are modified to be compatible with the newer release. However, as Rust is fairly commited to semver I don't see much use in this UNTIL there is a new major release.