I can’t force other people not to use changes, which means I will always need the latest version of rustc installed if I want to be able to build a relatively complete selection of the corpus of Rust code, which in turn makes it very difficult if not impossible for rust software to be distributed in typical OS package managers.

I.e., imagine how Debian or Ubuntu could package things if the definition of C++ changed every six weeks, given that the compiler version should change as little as possible during a major OS version cycle? This is a major blocker holding Rust back from mainstream adoption, IMO.