How about providing the following as part of this:

1. the option of a control file within that default path, to be able to specify subdirectories to be ignored. So anyone who already happens to have a ~/cl/ with a bunch of inactive subfolders with .asd files can make ~/cl/subdirs-to-exclude.asdc whose contents could be e.g.

  ("inactive-proj-1" "inactive-proj-2")

2. When registering systems in the default location, loudly announce that this is happening, e.g:

  *****

    Automatically registering .asd systems under ~/cl/... 

   Protip: if you want to exclude certain subdirectories, create file 

     ~/cl/subdirs-to-exclude.asdc

      containing a list of the subdirectory names to be excluded, e.g.

       ("inactive-proj-1" "inactive-proj-2")

  *****