That's a great idea!I think we can use Wikidata to build the list:http://tinyurl.com/zwdbzyq
I had been erroneously thinking along the lines that we'd have to be uploading something to the items before making it part of a Wikisource collection, but of course that's not necessary. I think your hierarchy of wikisource collections sounds perfect.
It'd be cool if items with a page on a Wikisource could have a little footnote like they do for Open Library ones ("This book has an editable web page on Open Library.).