That looks like a (unnecessary) complexity. Assume, there's a foo.bar static module and then some deployment configures a module named foo.bar within it's jboss-deployment-structure.xml. I haven't looked at JBoss Modules implementation and how it interacts with the module loaders, but how would it know that foo.bar "already exists" as a static module?
A module alias should be unique, if a deployment defines an alias of an already existing module it should fail. System modules cannot have dependencies on deployment modules.