I'm requesting a revert of the removal of wfMemckey for time being, because it blocks deployments on translatewiki.net as it's still being used by two extensions we use (TwnMainPage and PageForms).
Quoting Stable interface policy:
Code MUST emit hard deprecation notices for at least one major MediaWiki version before being removed. It is RECOMMENDED to emit hard deprecation notices for at least two major MediaWiki versions. EXCEPTIONS to this are listed in the section "Changes without deprecation" below.
I am not mistaken, wfMemckey was never hard-deprecated.