In terms of sources in Wikidata, and an ecosystem of Wikidatas, I wonder if you could have a look at the 'Economics' wiki, subject page at WUaS, - http://worlduniversity.wikia.com/wiki/Economics (accessible here at WUaS's main, Subjects' page - http://worlduniversity.wikia.com/wiki/Subjects - and based on this template currently -  http://worlduniversity.wikia.com/wiki/SUBJECT_TEMPLATE) - in terms of book citations and references and Wikidata. The 'Economics' page is a good, WUaS example of a MIT OCW- and Yale OYC-course-centric, academic, growing, subject page, which soon might divide into a Micro- and Macro-economics' wiki subject page, for example. How would such Wikidata ecosystem articulations of citations and references emerge in all 7,105 languages, for  example? WUaS is currently usually the American Anthropological Association citation practices, but with WUaS in Wikidata, I'm assuming these citation practices will/could occur in MediaWiki and SemanticWiki. As a real life example of a potential Wikidata, how would WUaS's Subject pages' book citations, and related, find form in the emergent ecosystem of Wikidatas?

(WUaS seeks to become the MIT / Harvard of the internet and in all 7,105+ languages and 204+ nation states, and such book citation practices, and related, will obviously be a foundation, and, again, just received the 'green light' from the state of California to begin the accreditation process, toward online, C.C., MIT OCW-centric, university degrees, first in English).

Cheers and thanks, 

Scott