I'm curious what the concern is with the rust editions mechanics in place. Each crate gets to define the language edition it is compiled with. Even if dependencies up convert to later editions they can still be linked against by crates that are an older edition.

As for the broader crate ecosystem, if crates you depend on drop support for APIs you depend on, that could cause you to get stuck on older unsupported releases. Though that is no different of a problem than any other language.