Allow a number of wikis to share a "content" namespace with wikitext. The namespace would:
# look local:
#* browsable, readable as a local namespace for all purposes,
#* editable without leaving your wiki (either by shared DB table or remote editing via CORS);
# live centrally:
#* on an actual wiki or just a database without its own interface,
#* as long as any update is immediately reflected on all consumers.
Example of possible use cases:
* Docs, like [[mw:Help:Contents]] and [[m:Help:Help]] (cf. bug 43591)
* Policies and guidelines + discussions about them, e.g. [[m:Category:Wikimedia policies and guidelines]] (only a handful pages but important)
Proposal by Rd232 at https://meta.wikimedia.org/?oldid=3467184: «a Meta: namespace which is accessible across all Wikimedia projects (in the same way that Commons files are accessible everywhere in the File: namespace) [...] home on another coordinating wiki, with which it can then share templates. [...] it's like InstantCommons, so we can call it InstantMeta [...]».
Note that the requirements are very different from bug 4547, which is about a) fetching, b) wikitext c) for local parsing (typically templates).
To be clear, I don't think this is ever going to happen. :)
Cf. [[https://lists.wikimedia.org/pipermail/wikimedia-l/2014-December/076014.html|Tim Starling on a similar proposal for files]], «I don't know what that would technically look like».