I see.
I know defining the specification is not a easy job; it is true for TL installer. Once xe choose scheme-full, then the dependencies of scheme-full will be inherited afterwards. Another notice is that, it is difficult to override scheme-full to make original scheme, say, for DVD-ROM because if the string of scheme-full is hide from tlpdb, the next year there may not install some collections/packages for lack of new dependencies.
Good,
-- Yusuke.