I think castget should implement the XDG Base directory specification1. This would mean moving the default location of the castgetrc to $XDG_CONFIG_HOME, if that's not set $HOME/.config. ~/.castgetrc could still be used as fallback location for backwards compatibility.

The directory ~/.castget would be moved to $XDG_DATA_HOME or if this is not set, $HOME/.local/share. For backwards compatibility, I'd suggest a mechanism which checks these directories exist in this order: $XDG_DATA_HOME/castget -> $HOME/.local/share/castget -> ~/.castget. The first directory found is used. If there is no directory found, create $XDG_DATA_HOME/castget, or (if not variable not set) $HOME/.local/share/castget.

I would really like this feature, since it would stop castget from clogging up my home directory.