Hi, regardless of whether Linux distros package rustc and cargo or not, I expect there will be a strong need to be able to easily install newer versionn of rustc and cargo without relying on the distro. I hope, in particular, that the Rust project will distribute, at least, properly-signed and maintained RPM and DEB packages of new versionn of rust and cargo from its own repository, that can be installed on a variety of Linux distros. See https://launchpad.net/~terry.guo/+archive/ubuntu/gcc-arm-embedded for an example of this which has worked great for me and others.
Debian Stable and Red Hat are notorious for maintaining old versions of packages way longer than anybody wants to support. With the great amount of improvement to rustc and Cargo, I think we’re actually 1 or 2 years away from being able to expect any Rust library or application author to support any version of Rust older than the latest stable release. I personally don’t want to be bothered by Linux distros asking me for free help in backporting changes or adding compatibility hacks to support old versions of rustc and Cargo that they ship. I imagine other people will feel similar. Having an official PPA operated by rust-lang.org would help ease this burden so that we can spend more time focusing on creating the future instead of maintaining the past.