First things first: the 1.21 release is rapidly approaching. Please look over https://www.mediawiki.org/wiki/Release_notes/1.21 and help update the documentation so that when release time comes, we will know about the work you've done on MediaWiki.
Next, I've started using the MW_release_status template on the documentation for MediaWiki releases, but I've run into a problem.
There are two different pages for newer releases. For example, 1.20 has https://www.mediawiki.org/wiki/Release_notes/1.20 and https://www.mediawiki.org/wiki/MediaWiki_1.20. Since the MediaWiki_1.20 page links to the RELEASE-NOTES-1.20 file, I didn't discover the Release_notes/1.20 page until later.
Older releases redirect from the MediaWiki_X.XX page to the Release_notes/X.XX page (see MediaWiki_1.15, for example). This makes it possible to use {{SUBPAGENAME}} to get the release number and display a proper message with the MW_release_status template.
For 1.21, I've made a redirect from MediaWiki_1.21 to Release_notes/1.21. I started to do something similar for 1.20, 1.19, etc, but stopped because I couldn't merge the pages quickly.
So, the question: is there a reason to keep two separate pages for each release going forward?