An interesting use of namespaces would be to relax orphan rules. This RFC states that nobody can write diesel-chrono crate that integrates the two crates that would like to stay independent of each other.
However, if there was diesel
chrono namespaced crate, then it would be known that all the diesel* crates are from the same author/owner/org, so they would have power to enforce their own orphan rules across their own crates.
This way the diesel crate could remain abstract and not depend on chrono, and the dieselchrono could add chrono support by being privileged to implement traits that currently only diesel can.