While on the Hackathon I had the opportunity to talk with some people from sister projects about how they view Wikidata and the relationship it should have to sister projects. Probably you are already familiar with the views because they have been presented already several times. The hopes are high, in my opinion too high, about what can be accomplished when Wikidata is deployed to sister projects.
There are conflicting needs about what belongs into Wikidata and what sister projects need, and that divide it is far greater to be overcome than just by installing the extension. In fact, I think there is a confusion between the need for Wikidata and the need for structured data. True that Wikidata embodies that technology, but I don't think all problems can be approached by the same centralized tool. At least not from the social side of it. Wikiquote could have one item for each quote, or Wikivoyage an item for each bar, hostel, restaurant, etc..., and the question will always be: are they relevant enough to be created in Wikidata? Considering that Wikidata was initially thought for Wikipedia, that scope wouldn't allow those uses. However, the structured data needs could be covered in other ways.
It doesn't need to be a big wikidata addressing it all. It could well be a central Wikidata addressing common issues (like author data, population data, etc), plus other Wikidata installs on each sister project that requires it. For instance there could be a data.wikiquote.org, a data.wikivoyage.org, etc that would cater for the needs of each community, that I predict will increase as soon as the benefits become clear, and of course linked to the central Wikidata whenever needed. Even Commons could be "wikidatized" with each file becoming an item and having different labels representing the file name depending on the language version being accessed.
Could be this the right direction to go?
Cheers, Micru