Wikidata allows to set a coordinate system - it is called a globe or coordinate system - on every coordinate. This would be the natural place to specify whether it is WGS84 or GDA94 or another system. Most of them are Q2, which, as per data model, is indeed WGS84.

https://www.mediawiki.org/wiki/Wikibase/DataModel#Geographic_locations 

Unfortunately this is currently not being displayed or edited in the UI, but the backend has the data. In theory.



On Tue, Oct 4, 2016 at 10:17 PM Sam Klein <sjklein@hcs.harvard.edu> wrote:
On Tue, Oct 4, 2016 at 2:01 AM, Joseph Seddon <jseddon@wikimedia.org> wrote:

> currently there is no clear indication within Wikipedia articles
> and as far as I can tell within Wikidata as to both what *datum* and what
> *version* any particular coordinate relates to, there is no guarantee that
> any particular coordinate would be any more correct than it was before.
>

This definitely should be fixed on the wikidata side.  Whether article
editors are savvy enough to know and enter this data is another question;
but at least the geotemplates should have fields for it and you can assume
that if those are empty some {person/bot hybrid} that understands that
nuance should fill them in.

~S
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