The proposed --expand-virtual-args option would be useful for modifying the behavior of commands such as 'emerge @system', in order to pull in packages referenced by virtuals directly in the @system set. For example, 'emerge --expand-virtual-args @system' would cause your libc implementation to be rebuilt (typically glibc), rather than just the virtual/libc package that references it via @system. Of course, the --expand-virtual-args option would also give analogous results for commands like 'emerge --expand-virtual-args virtual/libc'.