Have ManagedDeployableContainer/ManagedContainerConfiguration allow setting a read-only-server-config in arquillian.xml. StandaloneCommandBuilder.setServerReadOnlyConfiguration is already there, ready to apply the value to the server it launches.

One use case for this is configuring arq to use a file in WildFly's docs/examples/configs dir. A read-only-server-config can be located anywhere, while a plain server-config must point to a file in standalone-configuration.