I will try, and hopefully Micru (who knows Wikidata much better than me)

will follow up.

Wikidata right know is integrated with Wikipedia only.

Sister projects (as Wikisource) are now not taken in consideration, because each one is different and must be taken iin consideration indipendently. 

This is at least the opinion of the development tem (whom we speak to several times). 

One of the main issue is that, right know, 

Wikidata will store books metadata for Wikipedia pages, and that, in FRBR jargon, are "work" metadata (see http://en.wikipedia.org/wiki/Functional_Requirements_for_Bibliographic_Records)

Wikipedia articles, in most cases, talk about "books in general" ("The Hamlet", "Don Quixote", etc.).

Wikisource, on the other end, works with "editions" ("manifestation" in FRBR), which need more metadata 

(edition, year of the edition, language, translator, etc.)

This is the very same issues of djvu files on Commons, which store metadata into the Book template. 

Now, 

the problem is that, as I said before, Wikidata doen't talk with Commons and Wikisource (yet).

And it's a duty of the community to decide *how*, for example, store "edition metadata" in Wikidata.

We, for example, could create an item for every book edition we use in Wikisource/Commons. 

Or we could use *qualifiers*, and add these data in the main item related to the book.

The latter is Micru's proposal, and he made a mockup:

https://www.wikidata.org/w/index.php?title=Q4115189&oldid=35796153

I think it's the best proposal, as today, 

and if you agree you can support it:

https://www.wikidata.org/wiki/Wikidata:Requests_for_comment/References_and_sources#How_to_store_edition_data

I hope this clarification helped a bit.

Aubrey