I have to imagine that the reason why is that Wikivoyage is the closest project to Wikipedia out of all of the sister projects in many important ways. Yes, their page organization system is a little bit different, but not as different as say Wikisource, but perhaps more importantly, the kind of information that they would want as structured data is closest to the kind of information at Wikipedia wants in structured data. It is a safe choince and means less developer time has to be spent on bringing in the new project, so more developer time can be kept on Wikidata development itself.

On Jun 29, 2013 9:23 AM, "Federico Leva (Nemo)" <nemowiki@gmail.com> wrote:
legoktm, 28/06/2013 23:45:
Hi Denny,
I'm really excited to see a sister project getting included,

I've no idea why start with Wikivoyage, but it's very good that the central interwiki management is being extended to other projects when it's easy to do so (as it would be for Wikiquote and, mutatis mutandis, Commons).


however I'm
concerned that the community needs a bit more time and notice (I didn't
see anything about this on WD:PC). When importing interwiki links for
Wikipedias, we had a few months before they were used on client sites.
The proposed schedule gives our bots ~3 days to import a majority of
links, which I don't think is enough time. A whole week would be much
better in my opinion.
I've also started a page on-wiki to help coordinate the migration:

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