First look, I see that the incubator wiki has Wikibase Client installed, and they are site-linked, most likely they are able to access Wikidata.

@Ifeatu_Nnaobi_WMDE can confirm that incubator wikis can already use Wikidata. Tested on https://incubator.wikimedia.org/w/index.php?title=Wp/bom/12&action=submit by adding {{ #Property:P31 | from=Q2 }}.

Incubator can use data from Wikidata, but currently Wikidata does not support Incubator pages be used as a sitelink. So in Incubator there is a template {{INTERWIKI}} added to pages which reads sitelinks from manually-specified items and append it to page. Since Wikibase does not know what "current item" is when parsing a page, the QID must be manually specified in each template using Wikidata data ({{INTERWIKI}} is technically one of which).

Cf: T54971: [Goal] Sitelinks and arbitrary accesses to Incubator, OldWikisource and BetaWikiversity

In T437702#12312517, @seanleong-WMDE wrote:

@Ifeatu_Nnaobi_WMDE can confirm that incubator wikis can already use Wikidata. Tested on https://incubator.wikimedia.org/w/index.php?title=Wp/bom/12&action=submit by adding {{ #Property:P31 | from=Q2 }}.

So you need to manually specify QID - plain {{#Property:P31}} will not work. The entire Incubator is currently treated as one single wiki like Meta and Commons (but with sitelink currently disabled).

@Bugreporter, thanks for the answer! I misunderstood the question.

So basically the request is to allow multiple pages on a client wiki to be connected to the same repo item? That would be cool, not only on Incubator, but also on OSM wiki (and in any other single-wiki, multiple-language setup, including local dev wikis). However, I don’t see how it has anything to do with the sites table migration. And it also needs to be tested very thoroughly, there are probably many bits and pieces that assume that a single wiki cannot have more than one page connected to a given item (mw.wikibase.getSitelink(itemId, globalSiteId) in Lua, where globalSiteId defaults to the current wiki, to mention just one example).

In T437702#12315012, @Tacsipacsi wrote:

So basically the request is to allow multiple pages on a client wiki to be connected to the same repo item? That would be cool, not only on Incubator, but also on OSM wiki (and in any other single-wiki, multiple-language setup, including local dev wikis). However, I don’t see how it has anything to do with the sites table migration. And it also needs to be tested very thoroughly, there are probably many bits and pieces that assume that a single wiki cannot have more than one page connected to a given item (mw.wikibase.getSitelink(itemId, globalSiteId) in Lua, where globalSiteId defaults to the current wiki, to mention just one example).

I believe this is not part of goals in parent task.

But if it’s not part of the goals, what is the goal of this task? That’s what the task description is about (although the task title is completely unrelated to the updated description).

Thank you for the discussion! We're moving to "done" as it seems that our sites table migration won't affect Incubator wikis for the moment.