At each stage of creation for a new/updated extension, documentation is created. Then a derivative is recreated at the next stage. The recursive documentation burden could be relieved with a cascade of documentation automation.
With documentation built into the source code in a GitHub Pull Request for an extension, a tool like Sphinx can generate a GitHub readme.md markdown document.
The GitHub extension for MediaWiki can reformat that readme.md for inclusion in MediaWiki. (or use the https://github.com/ProfessionalWiki/ExternalContent)
You'd want something like the MediaWiki template:extension to auto populate and insert into the a reconstituted Sphinx-generated readme.md content.
For our MediWiki documentation site... that was established in March 2007... we also want to integrate MantisBT bug management extension and the Discourse forum for support. (But updates to our site for the necessary Lua prerequisites have been... less than successful. So we use a more simplistic pre-Lua template.)
The documentation ecology is being further integrated with a extension to Discourse that auto-posts back to Pull Request threaded messages.
But all of this would be predicated on initial code having some internal documentation & the Pull Request submission triggering a cascade of documentation creation/synchronization. So I suppose it all start with the Extension API documentation.
An integrated look at flowing documentation through extension evolution should be outlined (if not explicitly defined, streamlined or automated) in this discussion: "blue sky" idea for an "extension" is floated, idea formally proposed, requirements specification, design, proof of concept, alpha test, revision, beta test, installation docs, user docs, public release, support, bugs & enhancements, incremental release cycle, obsolescence, retirement, archiving.
Much of the documentation should only be written once. But if there isn't a What to cascade the data, it may be written at each stage... creating an unbearable (and all-too-often, dodged) burden.