Hoi,
I am actively pushing the inclusion of books that are available from the Open Library. They will be by authors who are already known to Wikidata and the books will have either an ISBN or an identifier from for instance the Library of Congress.
The point to this is that we do not know if readable books are available from Wikisource. Consequently Wikisource becomes of less relevance to the Open Library because they DO make it known and knowable what books are available for readers.
Thanks,
GerardM