It looks like it would take a bit of rewriting the cargo and rust packages, as well as the component or meta-package being created, but a custom toolchain could be created, which could be registered with the rustup binary as the default toolchain. See here.

I'd like to cast my vote for inclusion in the repo. While I take the viewpoint that most software should be gotten through a distro's repos, proper tooling is very important. As this is the official rust toolchain installer, I think it's something that should be in the repo. Perhaps it can be installed as a programming.rust component?

Thanks DataDrake.