If I'm understanding your concern correctly, that's totally a part of the proposal: But we can do even better. In practice, while code will continue workin

If I'm understanding your concern correctly, that's totally a part of the proposal: But we can do even better. In practice, while code will continue working with an old metapackage version, people are going to want to upgrade. We can smooth that process by allowing metapackage dependencies to be overridden if they appear explicitly in the Cargo.toml file.