After some discussion in September, Quim created T480 in Phabricator[1]. Markus polished up the "Security Release" section of the Release checklist[2] and we agreed to use it as the process for security releases from now on.
Footnotes: [1] https://phabricator.wikimedia.org/T480
[2] https://www.mediawiki.org/wiki/Release_checklist#Security_Release_.28minor_v...