> Though I think my problem with rust is that they make breaking changes in their compiler and spec every release.

Can you bring specific examples? The stable version is not only actually stable, but when big changes happen you can also opt into previous edition's behaviour with one config line. Breaking spec every release really doesn't sound right.

As for unstable - distros could find that complicated, but distros don't have to ship unstable things, so that doesn't sound like a big problem.