Up until Maven 3.3.7 if a pom didn't specify the scm section, it would be inherited and extended with the artifactId by default. This mechanism could work for a couple of SCMs like svn and cvs, but for most it doesn't.
This kind of scm specific logic of extending the connection or URL doesn't belong in Maven core.
Instead we should say that scm marks this project as a valid release root.
The source repository page (mpir) should ask a specific Scm class for handling connections and urls in case of modules.