I prefer that the CI test everything, and that we not release broken nightlies, that adding more tools to the product we release requires giving them the same commitment as the existing tooling. Our users, for better or worse, expect nightlies to be highly reliable, and if we get into a mode where nightlies regularly don’t work that will be bad for Rust’s perception.
Another alternative is to pull these tools in-tree to avoid the painful submodule dance.